Excretory System

Question 1

Excretion

Answer 1

Process of removal of harmful, unwanted nitrogenous metabolic wastes from the body, to maintain homeostasis.

Question 2

Waste Production and need for excretion

Answer 2

2) Co2 and H2O - metabolism of carbohydrates, fats and proteins
3) Nitrogenous wastes like ammonia, urea, uric acid, etc. - metabolism of proteins and other complex nitrogenous compounds
4) Nitrogenous products become toxic if retained for too long or in higher concentration hence removed
5) Excretion helps in osmoregulation of the body - maintaining salt and water balance in the body

Question 3

Substances to be Eliminated

Answer 3

1) Carbon dioxide and water - produced during oxidation of glucose
- Carbon dioxide - through the lungs
- Extra water - in the form of sweat
2) Nitrogenous wastes - urea, uric acid and ammonia
3) Excess salts and water soluble vitamins (NaCl, B, C) - mainly through kidneys
4) Water - excess removed, also serves as a solvent to carry harmful materials out
5) Bile pigments - mainly yellow bilirubin, breakdown products of the haemoglobin and dead RBCs - extracted by liver cells and secreted into the bile juice - excreted by the urine

Question 4

Urea

Answer 4

1) Main nitrogenous waste produced in the body
2) Produced in liver due to deamination of amino acids to usable glucose and urea to be excreted
3) Highly poisonous and can cause death if allowed to accumulate in the blood to a certain extent
4) Excreted through the kidneys

Question 5

Excretory Organs

Answer 5

1) Kidneys - primary excreting organs eliminating nitrogenous waste from the blood and expelling it in the form of urine

Accessory excretory organs -

2) Skin - sweat primarily consisting of water and NaCl and small amounts of urea nad lactic acid
3) Lungs - carbon dioxide through expired air
4) Liver - detoxifies ammonia by converting it to urea; breaks down bad cholesterol, alcohol, nicotine and drugs

Question 6

Parts of the Urinary system

Answer 6

1) Kidneys
2) Ureter
3) Urinary bladder
4) Urethra

Question 7

Kidneys - Location

Answer 7

Located on either side of the vertebral column, in the dorsal part of the abdomen, protected by the last two ribs
Right kidney slightly lower than the left kidney - to accommodate the large lobe of the liver

Question 8

Kidney - Function

Answer 8

1) Excretion of urea and other nitrogenous waste

2) Osmoregulation - Maintenance of the salt and water balance of the body

Question 9

Kidneys - Basic Structure

Answer 9

1) Two bean-shaped organs 10cm long and 6cm wide
3) Front end of ureter is expanded into the kidneys and called the pelvis
4) Urine produced in the kidneys constantly flow

Question 10

Ureter - Location

Answer 10

arises from the hilum (notch) in the median surface of each kidney and connects behind the urinary bladder

Question 11

Ureter - structure

Answer 11

1) Tube through which urine from the kidneys is constantly flowing
2) The front end of the ureter is somewhat expanded into the kidney and is known as the pelvis
3) Openings of the ureter into the bladder act as valves to prevent backflow of urine when the bladder contracts to pass out urine

Question 12

Ureter - Function

Answer 12

Conducts urine from the kidney to the urinary bladder

Question 13

Urinary Bladder - location

Answer 13

lower part of the abdomen

Question 14

Urinary bladder - function

Answer 14

temporarily stores urine and intermittently expels it out of the body through the urethra

Question 15

Urethra - function

Answer 15

expels urine from the urinary bladder out of the body

Question 16

urination or micturition

Answer 16

1) Expulsion of the urine from the urinary bladder out of the body through the urethra under an impulse sent by the brain
2) urine passes from the collecting ducts to the pelvis and from there through to the ureter into the urinary bladder
3) occurs due to ureteral peristalsis and due to gravity
4) sphincter muscles at the opening of the urinary bladder into the urethra relax only at the time of urination to allow the urine to pass out

Question 17

Kidney Tubules or nephrons

Answer 17

1) structural and functional unit of the kidney

2) a.k.a. uriniferous tubules or renal tubules

Question 18

Kidney tubule - structure

Answer 18

consists of: -

1) Bowman’s capsule
2) proximal convoluted tubule (PCT) or first convoluted tubule
3) Loop of Henle
4) Distal convoluted tubule (DCT)

Question 19

Bowman’s capsule

Answer 19

1) Thin-walled, single-cell thick epithelial cup
2) Hollow internal space continues as a tubule
3) Outer concavity has a knot-like mass of blood capillaries called glomerulus
4) Malpighian capsule - bowman’s capsule + glomerulus

Question 20

Proximal convoluted Tubule (PCT)

Answer 20

Starting convoluted region of the tubule before the loop of henle

Question 21

Loop of Henle

Answer 21

1) part of the tubule shaped like a hairpin
2) it is not convoluted
3) it runs in the medulla to turn back and re-entre the cortex to the form the next convoluted region (DCT)

Question 22

Distal convoluted tubule (DCT)

Answer 22

1) end part of the kidney tubule
2) Lies in the renal cortex
3) opens into the collecting duct which receives the content of many kidney tubules and pours it as urine into the pelvis of the kidney

Question 23

Internal Structure of a Kidney

Answer 23

1) outer darker cortex and inner lighter medulla
2) renal cortex - Bowman’s capsule, PCT, DCT
3) Renal medulla - loop of Henle and collecting duct
4) renal cortex has a dotted appearance due to presence of bowman’s capsules, glomerulus and PCT of numerous nephrons
5) Renal medulla has a striped appearance due to the presence of loops of Henle and collecting ducts of numerous nephrons
6) Part of the nephrons in the medulla are arranged into striped conical pyramids
7) apex of the pyramid projects into the pelvis of the kidney - Papilla
8) cortical tissue extend between adjacent renal pyramids - renal columns

Question 24

Blood supply to kidney tubules

Answer 24

1) pair of renal arteries branch of from the dorsal aorta to the respective kidneys
2) renal arteries branch and re-branch to give arterioles - enter the Bowman’s capsule as afferent arterioles
3) afferent arterioles break into many capillaries which form a knot-like mass - glomerulus - closely fitted inside bowman’s
4) capillaries reunite and emerge from the bowman’s as the efferent arteriole
5) efferent arteriole emerges from the bowman’s and breaks up into a secondary capillary network - vasa recta - surrounding the renal tubule
6) they rejoin to form a venules which after uniting with other venules of the kidney form the renal vein
7) renal vein leaves the kidney at the median surface and pours blood into the posterior vena cava

Question 25

Renal artery

Answer 25

1) brings oxygenated blood from the aorta to the kidney

2) contains more urea

Question 26

Renal vein

Answer 26

1) carries deoxygenated blood from the kidney to the posterior vena cava
2) contains less urea

Question 27

Production of urine - main procedures

Answer 27

1) ultrafiltration
2) selective reabsorption
3) tubular secretion

Question 28

Ultrafiltration

Answer 28

1) process by which blood plasma is filtered through the glomerulus under extraordinary hydrostatic pressure due to difference in the thickness of the wider afferent arteriole and the narrower efferent arteriole
2) almost al the blood plasma along with most of its organic and inorganic components passes out of the glomerulus into the funnel-shaped cavity of the bowman’s capsule
3) fluid entering the renal tubule is called the glomerular filtrate - consists of water, urea, salts, glucose and other plasma solutes
4) thicker part of blood left back in the glomerulus and proceeds toward the efferent arteriole
5) blood proceeding through the efferent arteriole is relatively thick and has - blood corpuscles, proteins and other large molecules

Question 29

glomerular filtrate

Answer 29

liquid collected during ultrafiltration in the glomerulus that is collected by the bowman’s capsule

Question 30

Selective reabsorption

Answer 30

1) the process of reabsorption of water and useful substances such as glucose, sodium and other salts from the glomerular filtrate such that the normal concentration of blood is not disturbed
2) PCT - 2/3rd of water and glucose and sodium and chlorine ions
3) Loop of Henle - some water and sodium ions
4) DCT - remaining chloride ions and some water

Question 31

Tubular secretion

Answer 31

1) Secretion of potassium ions and other foreign chemicals including drugs like penicillin into urine, by the cells of the tubular wall in the DCT

Question 32

Urine

Answer 32

the filtrate formed after selective reabsorption and tubular secretion

Question 33

Physical Properties of Urine

Answer 33

1) Colour - clear yellow due to pigment urochrome. may vary with diet
2) Volume - 1-1.5 litres per day
3) pH - 5-8. protein diet make sit more acidic while vegetable diet makes it more alkaline
4) smell - ammonia-like due to bacterial activity
5)

Question 34

Constituents in urine

Answer 34

1) 95% water and 5% solid wastes dissolved in it
2) organic constituents -
- urea
- creatinine
- uric acid
3) inorganic constituents
- sodium chloride
- potassium chloride
- ammonia

Question 35

abnormal constituents in urine

Answer 35

1) blood cells - haematuria - due to infection in urinary tract, kidney stones or tumour
2) glucose - glycosuria - due to diabetes mellitus
3) albumin - albuminuria - high blood pressure or increased permeability of the bowman’s capsule due to bacterial infection
4) bile pigments - due to anaemia, jaundice or liver cirrhosis

Question 36

Diuresis

Answer 36

1) increased production of urine due to less secretion of the antidiuretic hormone by the posterior lobe of the pituitary gland
2) ADH controls the concentration of urine by water reabsorption
3) If ADH secretion is increased water reabsoprtion is more and urine produced is less, and vice versa

Question 37

Diuretics

Answer 37

substances which increase formation of urine

e.g. - liquid diets, alcohol, coffee, tea, etc.

Question 38

gout and kidney stones

Answer 38

1) gout caused by crystallization of uric acid and deposition in the joints
2) kidney stones are caused by excessive uric acid and salts like calcium oxalate when the kidneys are not working fully normally

• uric acid is less soluble in water and hence may crystallize

Question 39

osmoregulation

Answer 39

urinate lesser in summer than in winter and the urine passed is generally thicker
- more sweat in summer, more water reabsorbed