Excretory System Flashcards
Excretion
Process of removal of harmful, unwanted nitrogenous metabolic wastes from the body, to maintain homeostasis.
Waste Production and need for excretion
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
Substances to be Eliminated
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
Urea
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
Excretory Organs
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
Parts of the Urinary system
1) Kidneys
2) Ureter
3) Urinary bladder
4) Urethra
Kidneys - Location
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
Kidney - Function
1) Excretion of urea and other nitrogenous waste
2) Osmoregulation - Maintenance of the salt and water balance of the body
Kidneys - Basic Structure
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
Ureter - Location
arises from the hilum (notch) in the median surface of each kidney and connects behind the urinary bladder
Ureter - structure
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
Ureter - Function
Conducts urine from the kidney to the urinary bladder
Urinary Bladder - location
lower part of the abdomen
Urinary bladder - function
temporarily stores urine and intermittently expels it out of the body through the urethra
Urethra - function
expels urine from the urinary bladder out of the body
urination or micturition
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
Kidney Tubules or nephrons
1) structural and functional unit of the kidney
2) a.k.a. uriniferous tubules or renal tubules
Kidney tubule - structure
consists of: -
1) Bowman’s capsule
2) proximal convoluted tubule (PCT) or first convoluted tubule
3) Loop of Henle
4) Distal convoluted tubule (DCT)
Bowman’s capsule
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
Proximal convoluted Tubule (PCT)
Starting convoluted region of the tubule before the loop of henle
Loop of Henle
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)
Distal convoluted tubule (DCT)
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
Internal Structure of a Kidney
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
Blood supply to kidney tubules
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
Renal artery
1) brings oxygenated blood from the aorta to the kidney
2) contains more urea
Renal vein
1) carries deoxygenated blood from the kidney to the posterior vena cava
2) contains less urea
Production of urine - main procedures
1) ultrafiltration
2) selective reabsorption
3) tubular secretion
Ultrafiltration
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
glomerular filtrate
liquid collected during ultrafiltration in the glomerulus that is collected by the bowman’s capsule
Selective reabsorption
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
Tubular secretion
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
Urine
the filtrate formed after selective reabsorption and tubular secretion
Physical Properties of Urine
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)
Constituents in urine
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
abnormal constituents in urine
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
Diuresis
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
Diuretics
substances which increase formation of urine
e.g. - liquid diets, alcohol, coffee, tea, etc.
gout and kidney stones
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
osmoregulation
urinate lesser in summer than in winter and the urine passed is generally thicker
- more sweat in summer, more water reabsorbed
