19- EXCRETARY PRODUCTS THEIR ELIMINATION

CHAPTER NO.19 EXCRETARY PRODUCTS & THEIR ELIMINATION

A191

INTRODUCTIONll:EXCRETION:It is the elimination of metabolic waste products from the body to regulate the composition of the body fluids and tissues. Various types of metabolic waste (Excretory) products are nitrogenous waste material, (Ammonia in Aquatic Animals,Urea in Semi-Aquatic Animals and Uric Acid in Animals living in dry conditions},mineral salts, vitamins, hormones etc.

HUMAN EXCRETORY SYSTEM:It functions to remove waste products from the human body. The whole existing Excretory System is mesodermal, in origin. In Human, the Excretory System consists of A pair of kidneys x A urinary bladder A pair of ureters A urethra

1. KIDNEYS:Kidneys are reddish brown, bean shaped structures situated between the

levels of last thoracic and third lumbar vertebra close to the dorsal inner wall

of the abdominal cavity.

The size of each kidney is 10-12 cm {Length} 5-7 cm {Width} 2-3 cm {Thickness} and its weight is 120-170 g.The two kidneys are asymmetrical, the right being posterior to the left.

Each kidney has a groove called HILUM through which ureter, blood vessels

and nerves enter.Inner to hilum, is a broad funnel shaped space called Renal Pelvis with projections called Calyces.

The white fibrous connective tissue covering the kidney is called Renal

Capsule.Each kidney is differentiated into two regions:

(i) Outer-Cortex =

(ii) Inner-Medulla

At certain points, the cortex extends into medulla forming ‘Columns of Bertini’.

Medulla contains conical masses {pyramids} each extending into pelvis.The tip of pyramid is called Papilla.The major collecting ducts open at this point.

The spaces, larger and smaller, into which pyramids open are called Major and Minor Calyx.

ve NEPHRON:Each kidney has one million complex tubular structures called Nephrons. The Nephron is the structures and functional unit of kidney.The Nephron in human is of two types:

(i) CORTICAL NEPHRONS- These nephrons mainly lie in the renal cortex, form

about 85 per cent of total nephrons and the loop of Henle is too short and extends

only very little into the medulla. Vasa recta are lacking.

(ii) JUXTAMEDULLARY NEPHRONS- These nephrons lie in the inner margin of

cortex, form about 15 per cent of total nephrons and the loop of Henle is very long

and runs deep into the medulla. Vasa recta are well developed.

EACH NEPHRON CONSISTS OF THE FOLLOWING PARTS:

i) BOWMAN’S CAPSULE-It is a double walled and blind (closed) structure. The inner side of this capsule has modified squamous epithelial layer (Podocyte Layer).

Inside the capsule there is a bunch of capillaries called Glomerulus. These

capillaries are more permeable than other capillaries of the body, due to

presence of fine endothelial pores(fenetral). These capillaries arise from

different arteriole and join to form different arteriole.The Glomerulus along with Bowman's capsule is called malphigian body or Renal corpuscle.The endothelial lining of glomerular capillaries with basement membrane and podocyte layer of Bowman's Capsule, form Filtration Membrane .

ii) PROXIMAL CONVOLUTED TUBULE {PCT}- A tubule form a highly coiled network, is lined with columnar epithelium microvilli called Brush Border Epithelium. It increases surface area for absorption.

iii) HENLE’S LOOP-It is Hair-pin like and has two limbs-

DESENDING LIMB and ASCENDING LIMB

Descending Limb is permeable to water and impermeable to sodium salts.Ascending Limb is permeable to sodium but impermeable to water.

IV] DISTAL CONVOLUTED TUBULE {DCT}-It continues after ascending limb, which is also highly coiled tubular region. It’s

permeability can be altered by hormones Aldosterene and Vasopressin.

V] COLLECTING TUBULE-The DCT’s of many nephrons open into a straight tube called collecting duct. The water absorption occurs both from, tubule and ducts.there are 2 types of capillaries-network around Henle’s Loop.

1} Peritubular Capillary Network

2} Vasa Recta

The Peritubular Capillary network is present around both limbs of henle, in both

nephrons.Vasa recta is present only in the descending limb of Henle and is present only in the Juxtamedullary nephrons.

2. URETERS:The pelvis of each kidney is continued as a ureter and emerges out at Hilus. Ureter is along and muscular tube .Ureters of both sides extends posteriorly and opensinto the urinary bladder.

3. URINARY BLADDER:It is a thin walled, pear shaped; white transparent sac present in the pelvic cavity. It temporarily stores the urine.

4. URETHRA:It is a membranous tube, which conducts urine to the exterior. The urethral sphincters keep the urethra closed except during voiding of urine.

LET US KNOW WHAT WE HAVE LEARNT!

Part-A: Very Short Answer Type Questions:

a. Multiple Choice Questions:

1) Which one of these is not a part of uriniferous tubule (Nephron}?

a. Loop of Henle

b. Collecting Duct

c. Bowman's capsule

d. DCT

2) The projections of renal pelvis are called:

a. Hilum

b. Calyces

c. Medullary Pyramids

d. Renal Columns

3) The cells named Podocytes occur in:

a. Inner wall of Bowman's capsule

b. Outer wall of Bowman's capsule

c. In the wall of Glomerulus.

d. In the wall of Henle’s Loop .

4) Glomerulus and Bowman’s capsule constitute:

a. Nephrotome

b. Renal Corpuscle

c. Renal Capsule

d. Malphigian Tubule

b. Fill in the Blanks:

1) Each kidney has a groove called through which blood vessels andnerves enter.

2) Vasa Recta is present in Nephrons.

3) Bowman's capsule has a special type of cells called .

c. True/False:

a) Brush border Epithelium of PCT increases the surface area for Absorption.

b) Descending Limb of Henle’s Loop is more permeable to sodium salts and impermeable to water.

a. Multiple Choice Questions:

1) b. Collecting Duct-

2) b. Calyces

3) b. Outer Wall of Bowman's Capsule

4) b. Renal Corpuscle

b. Fill in the Blanks:

1) Hilum

2) Juxtamedullary Nephrons

3) Podocytes

c. True/False:

a) True

b) False; Reason: Ascending loop of Henle’s Loop is more Permeable to water,

rather descending limb is permeable to water and impermeable to sodium

salts.

Part-B: Short Answer Type Questions::

Q1. Write the names of all parts of Human Excretory System.

Q2. Differentiate between Cortical nephrons and Juxtamedullary Nephrons.

Q3. Explain two types of capillaries present in the Nephrons.

Part-C: Long Answer Type Questions:

Q1. Explain the Structure of a nephron with the help of well-labelled diagram.

Q2. Draw labelled diagram of internal structure of Human Kidney

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INTRODUCTION:URINE EORMATION:-Urine Formation in Kidney involves three main processes-GlomerularFiltration,Reabsorption and Secretion, that takes place in different parts of the Nephron.

ULTRA FILTRATION:-This is the first step in urine formation, in which filtration of blood is carried out by the glomerulus. Glomerular capillary pressure {45 mm of Hg} favours filtration through its 3 layers: i.e., the endothelium of glomerular blood vessels, the epithelium of Bowman's capsule and a basement membrane between these two

layers. Podocytes of Bowman's Capsule leave some minute spaces called filtration

slits or slit pores. Blood is filtered through these membranes that almost all

components of plasma except protein pass into lumen of Bowman's capsule, so it

is considered as process of Ultra Filtration.

GFR:-The amount of the filtrate formed by the Kidneys per minute is called

Glomerular Filtration Rate.GFR in a healthy individual is about 125 ml/ minute 180 litres per day.Only 1/5 of plasma (20%) gets filtered per unit time. It is about 120ml per minute (GFR) 125ml/min = 7.5 litre/nrs = 180 litre/day

REABSORPTION:- The amount of urine formed per day is 1.8litre i.e. 1% of 180

litre per day, which means 99% of GFR is reabsorption by the renal tubules. This

process is called reabsorption.The tubular epithelial cells in different segments of nephron perform this either by active or passive mechanisms.

Active:- Glucose, Amino acid, Heat.

Passive:- Nitrogenous waste water.

SECRETION:-The tubular cells secrete some substances like H*, KY and ammonia into the

filtrate, during urine formation. This tubular secretion is also an important step inthe maintenance of ionic and acid-base balance of body fluids.

COMPOSITION OF URINE:Normal Human Urine is pale yellow due to Urochrome pigment and aromatic in nature.Amount- 1.2 litre/day

pH — 6( 4.5-7),generally acidic

Urea — 2% (2g — 100 ml of water)

Salts — 2% (mainly NaCl) Man is ureotelic in Excretion Urine is temporarily stored in urinary bladder and finally expelled out through urethra. It is called micturition.

LET US KNOW WHAT WE HAVE LEARN!!

Part: A - Very Short Answer Types Questions:

a. M.C.Qs:

1. Which of the following is not a process of urine formation?

(a) Glomerular filtration

(b) Reabsorption

(d) Excretion

2. How many layers of glomerular epithelium are increased in filtration of blood?

(ajOne

(b)Two

(c)Three

(d) Four

3. What is the full form of GFR?

(a)Gomerular filterating unit

(b) Glomerular filteration rate

(d) Globulin filtrating rate

4. The pH of human blood is approximately:

(a)4

(b)5

(d)7

5. What is GFR in normal healthy person?

(a) 180 litre per day

(b) 150 litre per day

(d) 125 litre per day

b. TRUE/FALSE:

1. Podocytes are present in the epithelial lining of PCT.

2. PCT of nephron is the main site of selective reabsorption.

ANSWER KEY: PART-A

A. MCQs:

1. (d) Excretion

2. (c)Three

3. (b) Glomerular filtration rate

4. (c)6

5. (a) 180 litre per day

B. TRUE / FALSE:

1. False

2. True

PART-B SHORT ANSWERTYPE QUESTIONS:

1. What is GFR? Give its value in Human.

2. Give composition of Urine.

PART: C LONG ANSWER TYPE QUESTIONS:

1. Draw a well labelled diagram of internal structure of Nephron?

2. Write three steps of urine formation.

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INTRODUCTION:NEPHRON is the main structural and functional unit of kidney.A nephron is made up of renal corpuscle and renal tubules which help to produce urine as waste after the complex process of filtration.

FUNCTIONS OF THE TUBULES IN REABSORPTION A PROCESS Proximal Convoluted Tubule (PCT):

PCT is lined by simple cuboidal brush border epitheium which Nearly all the essential nutrients and 70-80 per cent

of electrolytes and water are reabsorbed by the segment. PCT also helps to

maintain the pH and ionic balance of the body fluids by selective secretion of

hydrogen ions, ammonia and potassium ions into the filtrate and by absorption of

HCO °s from it. Henle’s Loop Reabsorption in this segment is minimum. This region plays a_ significant role in the maintenance of high osmolarity of medullary interstitial fluid. The descending

limb of loop of Henle is permeable to water but almost impermeable to electrolytes.

This concentrates the filtrate as it moves down. The ascending limb impermeable

to water but also allows transport to electrolytes.

Distal Convoluted Tubule (DCT):Conditional reabsorption of Na* and water takes place in this segment. DCT is also capable of reabsorption of HCO °3 and selective secretion of hydrogen and Potassium ions and NH; to maintain the pH and Sodium- Potassium balance in blood.

Collecting Duct:This long duct extends from the cortex of the kidney to the inner parts of the medulla. Large amounts of water could be reabsorbed from this region to produce concentrated urine. It also helps to maintain the pH and ionic balance of the blood by selective secretion of hydrogen and potassium ions.

LET US KNOW WHAT WE HAVE LEARNT!

A. MCQs:

Q1. In which segment, maximum reabsorption occurred?

(a)PCT

(b)DCT

(c)Botha&b

(d)Henle’s Loop

Q2. In which segment , minimum reabsorption occurred?.

(a)PCT

(b)DCT

(c)Botha&b

(d)Henle’s Loop

Q3. Where does the reabsorption of Na* water takes place?

(a)PCT

(b)DCT

(c)Botha&b

(d)Henle’s Loop

Q4 Which limb is impermeable to water?

(a)Descending Limb

(b) Ascending Limb

(d)Henle’s Loop

Q5. In which part of tubule, urine is produced?

(a) PCT

(b)DCT

(d) Henle’s Loop

B. TRUE AND FALSE:

1. Collecting duct extends from the cortex of of the kidney to the inner parts

of the medulla .

2. The Ascending limb of loop of Henle is permeable to water.

3. PCT also helps to maintain the pH and ionic balance of the body fluids.

C. FILL UPS:

1. DCT is also capable ofreabsorption of st.

2. Concentrated urine is producedinthe

ANSWER KEY: PART-A

A. MCQs:

Q1. (a) HINT- PCT is lined by simple cuboidal brush border epithelium

which increase the surface area for reabsorption.

Q2. (d) HINT —loop of Henle is permeable to water but almost impermeable

to electrolytes.

Q3. (b) HINT- Conditional reabsorption of Na and water takes place in this segment.

Q4. (b) HINT- The ascending limb impermeable to water.

Q5. (c) HINT- . Large amounts of water could be reabsorbed from this region

to produce a concentrated urine.

B. TRUE / FALSE:

Q1. TRUE HINT- Collecting duct is the longest duct of Nephron.

Q2. FALSE HINT- The descending limb of loop of Henle is permeabie to water.

Q3. TRUE HINT- PCT do selective secretion of hydrogen ions , ammonia

and potassium ions into the filtrate and by absorption of HCO -; from it.

C. FILL IN THE BLANKS:

Q1. HCO’s HINT — It helps to maintain the pH and Sodium- Potassium

balance in blood.

Q2. Collecting Duct

Q1. Write differences in the PCT and DCT.

Q2. Where the maximum reabsorption occurred?

Q1. Draw a well labelled diagram of nephron?

Q2. Explain the formation of urine by Nephron?

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INTRODUCTION:Urine is concentrated and the water conserved in the kidneys with the help of loop of Henle helped by Vasa Recta and flow of Urea. Loop of Henle and Vasa Recta form

COUNTER —CURRENT mechanism of urine concentration.Couter-current means flowing of fluids in two types of antiparallel channels as loop of Henle and Vasa Recta.

Urine is pale yellow coloured hypertonic fluid due to presence of urochrome pigment.

It is acidic in nature and has pH 6.0.

MECHANISM OF CONCENTRATION OF FILTRATE:

Mammals have the ability to produce concentrated urine. Tne Henle's loop and vasa recta play a significant role in this process. The flow of filtrate in the two limbs of Henle's loop is in opposite directions and thus forms a counter current mechanism.The flow of blood through the two limbs of vasa recta is also in a counter current pattern. The proximity between the Henle’s loop and vasa recta, as well as the

counter current, help in maintaining an increasing osmolarity towards the inner

medullary interstitial fluid, i.e., from 300mOsmol/L in the cortex to about

1200mOsmol/L in the inner medulla.This gradient is mainly caused by NaCl and Urea.

NaCl is transported by the ascending limb of Henle’s loop which is exchanged with

the descending limb of vasa recta.NaCl is returned to the interstitium by the ascending portion of vasa recta. Similarly,

small amounts of urea enter the thin segment of the ascending limb of Henle's loop which is transported back to the interstitium by the collecting tubule.

The above described transport of substances facilitated by the special arrangement

of Henle's loop and vasa recta is called the counter current mechanism.This mechanism helps to maintain a concentration gradient in the medullary interstitium. Presence of such interstitial gradient helps in an easy passage of water

from the collecting tubule, thereby concentrating the filtrate (urine).

Human kidneys can produce urine nearly four times concentrated than the initial

filtrate formed.

A. MCQs:

Q1. Which of the following plays a significant role in the concentration of

urine?

a) Henle's loop and vasa recta.

b) PCT and DCT

c) Glomerulus and Bowman's capsule

d) Collecting duct and tubule

Q 2. What is the osmolarity of the urine in the cortex?

a) 300mOsmol/L

b) 600mOsmol/L

c) 900mOsmol/L

d) 1200mOsmol/L

Q 3. Which of the following structure make the countercurrent

mechanism?

a) Henle's loop and glomerulus

b) PCT and DCT

c) Henle's loop and vasa recta

d) vasa recta and collecting duct.

Q 4. Which of the following is not a feature of a counter current

mechanism?

a) Helps in maintaining the concentration gradient

b) Helps in making the passage of water easier

c) Helps in concentrating the urine

d) Helps in diluting the urine

Q 5) Which of the following returns NaCl into the interstitium?

a) Ascending loop of Henle

b) Descending loop of Henle

c) Ascending portion of vasa recta

d) Descending portion of vasa recta.

B. TRUE —FALSE:

1. The gradient of Osmolarity is mainly caused by NaCl.

2. PCT and DCT play a significant role in the concentration of urine.

3. The Osmolarity of the urine in the cortex is 300mOsmol/L.

C. FILLIN THE BLANKS:

1. ............make the countercurrent mechanism.

2. ..........retums NaCl into the interstitium.

A. MCQs:

1) (a )Hint. Mammals can produce concentrated urine. The Henle's loop and

Vasa recta present in mammals play a significant role in the concentration

of the urine.

2) (a )Hint. The Osmolarity of the filtrate in the cortex is about 300mOsmol/L

while in the inner medulla it is 1200mOsmol/L. In the inner medulla, urine is four times more concentrated than the initial filtrate.

3) (c) Hint. The specialized arrangement of Henle's Loop and Vasa Recta enhances the transport of substances and helps in concentrating the urine is known as counter current mechanism.

4) (d) Hint. Countercurrent mechanism helps to maintain concentration gradient in medullary interstitium. The presence of such interstitial gradient helps in easy passage of water from the collecting tubule and therefore helpsin concentrating the urine.

5) (c) Hint. NaCl is returned to interstitium by the ascending portion of vasa recta just like NaCi, small amounts of urea are also transported back to the

interstitial fluid by collecting tubule.

B. TRUE / FALSE:

1. FALSE:

REASON: The osmotic gradient is mainly caused by Nacl and urea. Nacl is

transported by ascending limb of Henle's loop which is exchanged with the

descending limb of the vasa recta.

2. FALSE:REASON:Henle's loop and vasa recta plays a significant role in concentration

of urine.

3. TRUE:REASON: The osmolarity of urine in the cortex is 300mOsmol/L while in the

inner medulla it is 1200mOsmoil/L.

C.FILL IN THE BLANKS:

1. Henle's loop and vasa recta.

2. Ascending portion of vasa recta.

Q1.What is meant by counter current?

Q2. What is the significance of proximity of Henle's loop and vasa recta?

Q3. What is the cause of osmotic gradient?

Q1. Give the mechanism of concentration of filtrate in human kidney.

A195

OSMOREGULATORY ROLE OF KIDNEYS

Osmoregulation or regulation of osmolarity is the process which regulates the

concentration and osmotic pressure of blood by regulating the water contents of

blood plasma. It is an essential process as excessive loss of water may cause

dehydration while excess of water may dilute the body fluids.

FLEXIBILITY IN THE WORKING OF KIDNEYS: The vertebrate kidney is extremely flexible in its working. It excretes large amount of hypotonic urine when water intake

of an animal is very high, while it excretes small amount of hypertonic urine when water is deficient and needs to be conserved, this flexibility of working of renal tubules is best seen in land and marine animals especially in the birds and the mammals.So, osmoregulation maintains fluid balance and the concentration of electrolytes.

WHEN EXCESS OF WATER IN THE BODY FLUIDS:

Excess of water in body fluids lowers the osmotic pressure of the blood and

increases the blood volume.Excess or deficiency of water in the body fluids is noticed by osmoreceptors of hypothalamus which are sensitive to changes in blood volume, body fluid volume and ionic concentration.In EXCESS WATER cases, the urine passed out of the body is hypotonic to expel the excess of water. It involves two processes:

(a) Increased ultrafiltration: Excess of water in the body fluids increases the

hydrostatic pressure which increases the rate of ultrafiltration and more nephric

filtrate is formed. GFR (Glomerular Filtration Rate) increases.

(b) Decreased reabsorption:ROLE OF ADH IN OSMOREGULATION:The permeability of wall of the DCT (distal convoluted tubule) and collecting tubules is controlled by anti-diuretic hormone, ADH or vasopressin hormone secreted by hypothalamus of brain and released from the posterior lobe (neurohypophysis) of pituitary gland.

ADH also has constrictor effect on blood vessels.Increase in water level in the body fluid and so increase in blood volume switches off the osmoreceptors which decreases the release of ADH from posterior pituitary.Low ADH level lowers the permeability of wall of DCT and collecting tubules which decreases reabsorption of Water. So a large amount of hypotonic urine is excreted out and volume of body fluids becomes normal.But when the volume of body fluids decreases below normal due to excessive bleeding, profuse sweating during heavy exercise or high environmental

temperature, then reverse occurs. Less ultrafiltration and more reabsorption

produce small amount of hypertonic urine which increases the volume of body fluids

to normal.If there is deficiency of ADH, a disease called diabetes insipidus is caused which is characterised by diuresis (increased urine output, about 10 times more than the normal rate), polydipsia etc. but urine is sugar free.

ROLE OF RENIN - ANGIOTENSINOGEN-ALDOSTERONE

SYSTEM (RAAS) INOSMOREGULATION:RAAS is a multi hormonal system that is involved in the regulation of plasma sodium concentration and arterial blood pressure.

Kidneys also regulate the degree of reabsorption of water from the nephric filtrate by regulating Na concentration in interstitial fluid through a Renin-Angiotensinogen system (explained by Tigerstadt and Bergman - 1898), under the control of JUXTA GLOMERULAR APPARATUS of the kidney. When GFR, BP and Blood Volume

decreases, the NE of DC) is (ct stimulated which activates the JG cells, present in the walls of Afferent Arteriole and Efferent Arteriole of Glomerulus

of Kidney to produce RENIN.Now RENIN converts the hormone ANGIOTENSIN (which is secreted by liver and present in blood plasma) to ANGIOTENSINOGEN - I.

Angiotensinogen —| is converted to ANGIOTENSINOGEN-II with the help of ACE,

Angiotensin Converting Enzyme, secreted by LUNGS.Angiotensin4l is a highly powerful vasoconstrictor which increases glomerular

blood pressure and GFR.It acts on adrenal cortex to release ALDOSTERONE, which acts on DCT and helps in reabsorption of water those results in hign BP and HIGH blood volume. It also acts on PCT.

ROLE OF ATRIAL NATRIURETIC FACTOR (ANF) IN

OSMOREGULATION:Atrial Natriuretic Factor (ANF) is a polypeptide hormone secreted by the cardiac muscles of wall of Atria of heart. It promotes water loss due to excessive urination. So it opposes the function of ADH.It is secreted in response to increased blood volume and blood pressure.It is antagonistic to RAAS and inhibits the release of RENIN from the

juxtaglomerular cells and hence Angiotensinogen not produced, so reduces the secretion of aldosterone and reabsorption of NaCl of nephric filtrate into the interstitial fluid.So ADH, RAAS and ANF regulate the functioning of kidney tubules by feedback mechanisms to regulate the osmolarity, salt concentration, blood

pressure and blood volume, called homeostasis.

LET US KNOW WHAT WE HAVE LEARNT!!

PART: (A) VERY SHORT ANSWER TYPE QUESTIONS:

A. MCQs:

1. Which of these is not active osmoreceptor?

a) Blood volume

b)Body fluid volume

c) Homeostasis

d) lonic concentration

2. What is another name for ADH?

a) Oxytocin

b) Noradrenalin

c) Vasopressin

d) Ghrelin

3. Where is vasopressin released from?

a) Neurohypophysis

b) Pituitary gland

c) Adrenal gland

d) Pancreas

4. When water intake of an animal is very high it excretes large amount of ?

a) Hypotonic Urine

b) Hypertonic Urine

c) lsotonic Urine

d) None of these.

5. Which of these is not a function of ADH?

a) Stimulates water reabsorption

b) Decreases blood pressure

c) Prevents diuresis

d) Decreases perspiration

B. Fill Ups:

1. Flexibility of working of renal tubules are best seen in and animals.

2. Animals excrete small amount of urine when water is deficient and needs to be conserved.

C. True/False:

1. Osmoreceptors are not sensitive to change in blood volume.

2. ADH is called vasopressin hormone.

3. ADH helps in osmoregulation.

ANSWER KEY: PART-A

A. MCQs:

1). c; Homeostasis.

2). c; vasopressin.

3). b; pituitary gland.

4). a; hypotonic urine.

5). b; decreases blood pressure.

B. Fill Ups:

1). land and marine.

2). hypertonic urine

C. True/False:

1). False

2). True

3). True

PART (B): SHORT ANSWER TYPE QUESTIONS:

1. What is the role of RENIN-ANGIOTENSINOGEN-ALDOSTERONE SYSTEM

(RAAS)?

2. How diabetes insipidus disease is caused?

3. What is Arterial Natriuretic Factor (ANF)?

PART (C): LONG ANSWER TYPE QUESTIONS:

1. Write down the role of ADH in osmoregulation.

A196

INTRODUCTION:Urine is produced and drained continuously by the nephrons present in

kidneys into the renal pelvis, from here, it is carried down to the ureters and

then into the urinary bladder. When the urinary bladder gets filled up to its

capacity then we feel an urge to expel it out of the body.

What is Micturition?

Micturition is the process where urine is expelled from the body. Animals and Humans have a specialized system of organs known as the Excretory System to eliminate the waste products from the body. In other words, the process of expelling urine from the body is called Micturition.

x MICTURITION PROCESS:Micturition is the process of discharging urine from the Urinary Bladder.Micturition process consists of two phases:

Storage Phase

Voiding Phase

& STORAGE PHASE:The Urinary Bladder is a balloon-shaped, hollow, muscular, organ that acts as the Storage organ for Urine. The Urinary Bladder in a healthy urinary

system can store up to 16 ounces of urine for 2 to 5 hours easily. The circular sphincter muscles prevent leakage of urine. They tightly close around the opening of the bladder into the urethra that allows the passage of urine outside the body.

VOIDING PHASE:When the Bladder is filled with urine, the nerves in it are triggered and there is an urge to urinate. The brain signals Urinary Bladder to contract. The

stretch receptors of the urinary bladder send a signal to the Central Nervous

System (CNS) in response to which the nervous system sends a signal that

incites the contraction of the urinary bladder. Through the urinary opening at

the urethra, the urine is eliminated, and the process is called Micturition The

neural mechanism involved is called the Micturition reflex.

LET US KNOW WHAT WE HAVE LEARNT!

PART-A: VERY SHORT ANSWER TYPE QUESTIONS:

a. MULIPLE CHOICE QUESTIONS:

1} Urine is formed by:

a. Nephron

b. Urinary Bladder

c. CNS

d. PNS

2} Urine formed by nephrons is carried to:

a. Nephrons

b. Urinary Bladder

c. Henle’s Loop

d. Vasa Recta

3} Which body part initiates the signal for urination?

a. Urinary Bladder

b. CNS

c. Nephron

d. PNS

4} Which receptors are present on the walls of the bladder?

a. Stretch

b. Relax

c. Contract

d. Compass

5} Which organ starts stretching after receiving the signal from CNS?

a. Henle’s Loop

b. Vasa Recta

c. Urinary Bladder

d. Nephrons

b. TRUE/FALSE:

1] Urine is formed by nephrons.

2] Signal is initiated by stretching of urinary bladder.

3] Relax receptors are present on the walls of the bladder.

c. FILL IN THE BLANKS:

1} stores urine inside it.

2} The process of release of urine is called .

A. Multiple Choice Questions:

1} (a) Nephron

2} (b) Urinary Bladder

3} (b) CNS

4} (a) Stretch

5} (c) Urinary Bladder

B. True/False:

1] True

2] True

3] False Reason: Stretch receptors are present on the walls of the Bladder.

C. Fill in the Blanks:

1} Urinary Bladder

2} Micturition

Part-B: Short Answer Type Questions

1] Define Micturition?

2] What is Micturition Reflex?

3] Name two phases for Micturition?

Part-C: Long Answer Type Questions

1] How is Urine Released?

A197

Dear students, you know that the removal of waste products formed in the body is called EXCRETION.A pair of Kidneys is the n-main organ of excretion in our body.There are various other organs in our body that helps in excretion. These are;SKIN, LUNGS, LIVER and INTESTINE.

Let us discuss these one by one in detail.

1. EXCRETORY ROLE OF SKIN:Skin plays an important role in excretion in the mammals. Skin of mammals (e.g.,human beings) is glandular and is with two types of glands e.g., sebaceous glands (oil glands) and sudoriferous (sweat) glands.

(A)SWEAT GLANDS are highly vascular, simple, coiled, tubular glands.These separate a number of wastes, blood and throw them out in the form of sweat. Sweat is mainly formed of water (99%), inorganic salts(Chiefly sodium chloride), lactic acid, some urea and CO2:

Sweat performs two functions:

(i) Excretion of excess of salts and water; and

(ii) Evaporation of sweat causing cooling effect and helps in homeothermy.

Volume of sweat varies considerably from negligible to about 14 litres a day.Sweat amount increases with activity and environmental temperature. Sweating is mainly meant for cooling of body and not excretion.

(B)SEBACEOUS (OIL) GLANDS are branched saccular glands opening in hair follicles. These secrete an oily secretion, called SEBUM, formed of lipids like waxes, sterols, hydrocarbons and fatty acids. This secretion provides a protective oily coat over the skin.

2. ROLE OF LUNGS IN EXCRETION It is estimated that lungs expel about 18 litres of COz, per day (about 200 mL /minute) and about 400 ml of water per day in normal resting condition.Amount of water lost through lungs varies with:Climatic conditions: It is low in hot humid condition but is more in cold and dry

condition.Rate of ventilation.

3. ROLE OF LIVER IN EXCRETION:Liver is a multipurpose largest gland of the vertebrates. It helps in excretion in

the following ways;

(a)Formation of bile pigments (bilirubin and biliverdin) and urine pigment(urochrome) from the haemoglobin of dead RBCs.

(b) Changing the excessive and harmful amino acids into urea by urea or

ornithine cycle.

(e.g., vitamin C) and toxic drugs.

4. ROLE OF LARGE INTESTINE IN EXCRETION:

The cells of colon remove salts like calcium phosphate from the blood and

expel them out with faeces.

LET US KNOW WHAT WE HAVE LEARNT!!

A. MCQs: a

1. How much percentage of water is present in sweat?

a) 60

b) 70

c) 80

d) 99

2. Which one is not an excretory organ?

a) Skin

b) Kidney

c) Small Intestine

d) Liver

3. Evaporation of sweat causing cooling effect which is caused by:

a) Sweat Glands

b) Sebaceous Glands

c) Botha&b

d) None of these

4. Accessory excretory human organ is:

a) Skin and Stomach

b) Skin and Heart

c) Lungs and Appendix

d) Skin, Lungs, Liver and Large Intestine.

5. Bile pigments, Bilirubin and Biliverdin are formed by:

a) Liver

b) Lungs

c) Skin

d) Large Intestine.

B. Fill Ups:

1. is the largest gland.

2. A cyclic process of urea formation is called cycle

C. True/False:

1. Lungs expel about 28 litres of CO2 per day.

2. Evaporation of sweat causing cooling effect.

3. The Cells of the large intestine removes salt like Calcium Phosphate from

blood.

ANSWER KEY: PART-A

A MCQs:

1). d; 99%

2). c; small intestine.

3). a; sweat glands.

4). d; Skin, Lungs, Liver and Large Intestine.

5). a; Liver.

B. Fill Ups:

1). Liver

2). Ornithine

C. True/False:

1). False

2). True

3). True

PART (B): SHORT ANSWER TYPE QUESTIONS:

1. How skin helps in excretion?

2. Differentiate between sebaceous and sudoriferous glands.

3. Name two accessory excretory organs of man.

PART (C): LONG ANSWER TYPE QUESTIONS:

1. Write down the role of Lungs and Liver in excretion.

A198

INTRODUCTION:Disorders of Excretory System:

The excretory system is responsible for the elimination of wastes from the body of

an organism. Organs such as liver, kidney, skin and sweat glands eliminate the

nitrogenous waste from the body. Any disorder in the excretory system leads to the accumulation of nitrogenous wastes in the body that leads to certain diseases.

Let us have a detailed look at the different types of disorders of the excretory system.

Major Disorders of Excretory System:A list of the disorders of the excretory system is mentioned below:

1) UREMIA:

Under this condition, the urea accumulation is comparatively high. In such patients,excess urea is removed by hemodialysis.

2) HEMODIALYSIS:In hemodialysis, the blood is drained carefully from whichever artery is convenient and is sent to the dialyzing unit. The unit contains a porous membrane which allows passage of molecules on the basis of the concentration gradient.

Malfunctioning of kidneys can lead to accumulation of urea in blood, a condition

called uremia, which is highly harmful and may lead to kidney failure. In such

patients, urea can be removed by a process called haemodialysis. During the

process of haemodialysis, the blood drained from a convenient artery is pumped

into a dialysing unit called artificial kidney. Blood drained from a convenient artery is pumped into a dialysing unit after adding an anticoagulant like heparin. [ne unit contains a coiled cellophane tube surrounded by a fluid (dialysing fluid) having the same composition as that of plasma except the nitrogenous wastes. The porous cellophane membranes of the tube allow the passage of molecules based on

concentration gradient. As nitrogenous wastes are absent in the dialysing fluid, these substances freely move out, thereby clearing the blood. The cleared blood is

pumped back to the body through a vein after adding anti-heparin to it. This method is a boon for thousands of uremic patients all over the world.

A functioning kidney is used in transplantation from a donor, preferably a close relative, to minimise its chances of rejection by the immune system of the host.Modern clinical procedures have increased the success rate of such a complicated technique.

RENAL CALCULI OR KIDNEY STONES:Stone or insoluble mass of crystallised salts (oxalates, etc.) formed within the kidney.

Kidney stones are the result of the deposition of dissolved minerals or insoluble salts on the inner lining of the kidney. These increase in size and cause immense pain in the patients when passed.

GLOMERULONEPHRITIS:Inflammation of glomeruli of kidney is known as Glomerulonephritis.

“LET US KNOW WHAT WE LEARN?”

PART-A VERY SHORT ANSWER QUESTIONS

(a)MULTIPLE CHOICE QUESTIONS:

Q1. Which of the following can be cured by hemodialysis?

(a) Renal calculi

(b) Glomerulonephritis

(d) All of these can be cured by haemodialysis

Q2. Malfunctioning of kidneys is known as?

(a) Glomerulonephritis

(b) Renal failure

d) Renal calculi

Q3.Condition of stone formed within the kidney is known as

(a)Uremia

(b) Glomerulonephritis

(d) Renal failure

Q4. Inflammation of glomeruli of kidney is called as

(a) Angina pectoris

(b) Glomerulonephritis

(d)Uremia

Q5. Uremia affects which part of the body?

(a)Heart

(b) Eyes

(d) Kidney

(b)TRUE/ FALSE:

Q1. Uraemia is accumulation of urea in urine.

Q2. Kidney transplantation is the ultimate method in the correction of acute

renal failures (kidney failure).

Q3. The excretory system is responsible for the elimination of wastes from the

body of an organism.

(c)FILL IN THE BLANKS:

Q1. anticoagulant is used during haemodialysis in dialysing unit.

Q2. During haemodialysis, the blood drained from a convenient artery is pumped into a dialysing unit called

ANSWER KEY: PART-A

(a)MULTIPLE CHOICE QUESTIONS:

1. (c) Uremia

2. (b) Renal failure

3. (c) Renal calculi

4. (b) Glomerulonepnhritis

5. (d) Kidney

(b) TRUE /FALSE:

1. False

2. True

3. True

(c)FILL IN THE BLANKS:

1. heparin

2. artificial kidney

PART-B_ SHORT ANSWER TYPE QUESTIONS:

Q1.What are the effects of renal failure on human body?

Q2.Mention three major disorders of Excretory System?

Q3 Why kidney only from a close relative donor is preferred during kidney

transplantation?

PART-C LONG ANSWER TYPE QUESTIONS:

Q1. Explain the process of haemodialysis?

A199

RECAPITULATION:Many nitrogen containing substances, ions, CO2, water, etc. that accumulate in the body have to be eliminated. Ammonia, urea and uric acid are the major nitrogenous wastes excreted.

in humans, the excretory system consists of one pair of kidneys, a pair of ureters, a

urinary bladder and a urethra. Each kidney has over a million tubular structures

called Nephrons. Nephron is the functional unit of kidney and has two portions-

Glomerulus and Renal Tubule. The renal tubule has Bowman's capsule, Proximal

Convoluted Tubule {PCT}, Henle’s Loop {HL} and Distal Convoluted Tubule {DCT}.

Urine Formation involves three main processes, i.e., Filtration, Reabsorption and Secretion. About 1200 ml of biood is filtered by the Glomerulus per minute to perform 125 ml of filtrate in the Bowman's capsule per minute [GFR]. PCT is the major site of reabsorption and Selective Secretion. HL primarily helps to maintain osmolar gradient (300 mosmolL' to 1200 mosmolL"') within the Kidney interstitium.

DCT and collecting duct allow extensive reabsorption of water and certain

electrolytes, which help in osmoregulation: H*, K* and NH3 could be secreted into

the filtrate by the tubules to maintain the iconic balance and pH of body fluids.

A Counter Current Mechanism operates between the two limbs of the loop of Henle

and those of vasa recta (capillary parallel to Henle’s Loop). The filtrate gets

concentrated as it moves down the descending limb but is diluted by the ascending limb. Urine is stored in the urinary bladder till a voluntary signal from CNS carries out it release through urethra, i.e., micturition. Skin, lungs and liver also assist in excretion.

NCERT Exercises Questions and Solutions

Q 1. Define Glomerular filterationrate(GFR)

Ans :-The amount of the Filtrate formed by the kidneys per minute is called

Glomerular filteration rate(GFR)

Q 2. Explain the autoregularity mechanism of GFR

Ans:-The kidneys have built in mechanisms for this .One such efficient mechanism is

carried out by juxta glomerular apparatus(JGA).A fall in GFR can activate the JG

cells to release renin which can stimulate the Glomerular Blood flow and their by the

GFR back to normal .

Q 3. Indicate whether the following statements are true or false:

a) Micturition is carried out by a reflex.

Ans :-True

b) ADH helps in water elimination, making the urine hypotonic.

Ans:-False

c) Protein —free fluid is filtered from blood plasma into the Bowman's capsule.

Ans:-True

d) Henle’s loop plays an important role in concentrating the urine.

Ans:-True

e) Glucose is actively reabsorbed in the proximal convoluted tubule.

Ans:-True

Q 4. Give a brief account of the counter current mechanism.

Ans:- NaCl is transported by the ascending limb of Henle’s loop which is exchanged

with the descending limb of vasa recta. NaCl is returned to the interstitium by the

ascending portion of vasa recta.

Similarly small amounts of urea enter the thin segment of the ascending limb of

Henle’s loop which is transported back to the interstitium by the collecting tubule.

The above described transport of substances facilitated by the special arrangement

of Henle’s loop and vasa recta is called the counter current mechanism.

Q 5. Describe the role of liver, lungs and skin in excretion.

Ans:- LIVER -Liver ,the largest gland in our body ,secretes bile containing

substances like bilirubin ,biliverdin , cholesterol , degraded steroid

hormones,vitamins and drugs.Most of these substances ultimately pass out along

with digestive wastes .

LUNGS -our lungs removes large amounts of CO2 (approximately 200 ml per minute) and also significant amount of water everyday.

SKIN- The sweat and sebaceous glands in the skin can eliminate certain substances

through their secretion.

Q 6. Explain micturition.

Ans:-The CNS passes on motor messages to initiate the contraction of smooth

muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.

The process of release of urine is called micturition.

Q 8. What is meant by the term osmoregulation?

Ans:-lonic and fluid volume regulation is called osmoregulation.

Q 9. Terrestrial animals are generally either ureotelic or uricotelic, not an

ammonotelic. Why?

Ans:- Because terrestrial adaptation necessitated the production of lesser toxic

nitrogenous wastes like urea and uric acid for conservation of water.

Q 10. What is the significance of Juxta Glomerular Apparatus (JGA) in kidney

function?

Ans :- Juxta Glomerular Apparatus [JGA] is a special sensitive region formed by

cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact. The JGA plays a complex regulatory role. A fall in glomerular blood flow/ glomerular blood pressure/ GFR can activate the JG cells to release rennin which converts angiotensinogen in blood to angiotensinogen and further to angiotensinogen II. Angiotensinogen Il, being a powerful vasoconstrictor,increases the glomerular blood pressure and thereby GFR. Angiotensinogen II also

activates the adrenal cortex to release aldosterone. Aldosterone causes reabsorption

of Na+ and water from the distal parts of tubule.

Q 11. Name the following:-

a) A chordate animal having flame cells as excretory structures -Amphioxus

b) Cortical portions projecting between the medullary pyramids in the human

Kidney- Columns of Bertoli.

c) A loop of capillary running parallel to the Henle’s loop — Vasa recta

Q 12. Fill in the gaps:

a) Ascending limb of Henle’s loop is impermeable_ to water whereas the

descending limb is permeable to it.

b) Reabsorption of water from distal parts of the tubules is facilitated by hormone

ADH.

c)Dialysis fluid contain all the constituents as is plasma except nitrogenous waste (urea).

d) A healthy adult human excretes (on an average) 25 -30 gm of urea /day.

A200

RECAPITULATION:Dear students, we have learnt all about chapter no.19, now we are going to revise important questions and diagrams of this chapter.

ONE MARK QUESTIONS

Q1. Name three different types of excretory products in animals?

Ans.Ammonia, Uric acid and urea.

Q2. What is pH of human urine?

Ans. The pH of human urine is approximately

Q3. Which is known as antidiuretic hormone?

Ans.Vasopressin is known as antidiuretic hormone(ADH).

Q4.Where is the urea formed in the human body?

Ans. Inside the liver.

Q5. What is the main process of urine formation?

Ans.The main process is ultrafiltration, tubular reabsorption and tubular secretion.

Q6. Name two components of a Malphigian body?

Ans. Bowman s capsule and glomerulus together form the malphigian body.

Q7. Give the name of main components that plays an important role in the counter current mechanism?

Ans. Henle's loop and vasa recta.

Q8. How do lungs help in excretion?

Ans.Carbon dioxide and water are the waste products removed by the lungs in the

expired air.

Q9. What is the ratio of the concentrated filtrate to that of the initial filtrate?

Ans.The concentrated urine is nearly four times concentrated than the initial filtrate formed.

Q10.Which disorder is detected when glucose is present in urine?

Ans. Glycosuria.

TWO MARKS QUESTIONS:

Q1.Define glomerular filtration rate (GFR).

Ans. Glomerular Filtrate Rate or GFR, is the amount of filtrate formed by the

kidneys per minute. The glomerular filtration rate in a normal adult human is about 125 ml per minute and 180 litres of filtrate is produced daily.

Q2.What is micturition?

Ans.Micturition is a process of urine excretion from the urinary bladder. The

process of micturition consists of two phases- Storage phase and Voiding phase.

Q3.What is meant by the term osmoregulation?

Ans. Osmoregulation is the active regulation of the osmotic pressure of an

organism’ s body fluids, detected by osmoreceptors, to maintain the homeostasis

of the organism s water content, that is maintain the fluid balance and the

concentration of electrolytes.

THREE MARKS QUESTIONS:

Q1. Describe internal structure of Human Kidney?

Ans. The kidney is a reddish brown colored organ which is a bean shaped located

between the last thoracic and third lumbar vertebra near the Abdominal cavity. The

hilum is a notch which is present in the inner side of the kidney through which

ureter, blood vessels and nerves enter. The outer layer of kidney is a tough

Capsule. Inside the kidney, there are two Zones, an outer cortex and an inner

medulla. The medulla is divided into a few conical masses (medullary Pyramids)

projecting into the Calyces. The cortex extends in between the medullary Pyramids

as renal columns called Columns of Bertini. Each kidney has one million complex

tubular structures called Nephrons.

Q2. Give a brief account of the counter current mechanism?

Ans. Inside the kidney, counter current mechanism occurs for conservation of

water. Henle’s Loop is a U- shaped part of the nephron. The flow of blood in the

two branches of tube is in the opposite direction which gives rise to the counter

currents.Vasa recta, on the other hand is an efferent arteriole that forms a Capillary network around the tubules in the renal medulla which tracks parallel to the

Henle’s loop. Vasa recta is also U-shaped. The flow of blood is in opposite

directions in the two limbs of vasa recta. Hence, the blood that enters the renal

medulla in the descending limb comes in close proximity with the outgoing blood in

the ascending limb.Through the counter current mechanism, the osmolarity increases in the cortex from 300mOsmol/L to about 1200mOsmol/L in the inner medulla which helps in sustaining the concentration gradient. This in turn aids in the easy movement of water from the collecting tubules. The concentration gradient is due to the movement of urea and NaCl.

Q3. Describe the disorders of Excretory System?

Ans. Malfunctioning of kidneys can lead to several disorders of the excretory

system. Some are as follows:

(1)Uremia: It is the presence of an excessive amount of urea in the blood. Urea

is highly harmful as it poisons the cells at high concentration and may lead to

kidney failure.

(2)Kidney Failure: Partial or total inability of kidneys to carry on excretory and salt-water regulatory functions is called Renal or kidney failure.

(3) Renal Calculi: It is the formation of stone or insoluble mass of crystallized

salts (calcium, magnesium, phosphates and oxalates), formed within the

kidney.

(4)Glomerulonephritis: It is the inflammation of glomeruli of kidney.