homeostasis and kidney (C3)

Question 1

Homeostasis definition and examples

Answer 1

the maintenance of a constant internal environment within a living organism regardless of the external conditions e.g regulation of blood glucose levels, core body temp, solute potential etc… maintaining dynamic equilibrium

Question 2

Negative feedback

Answer 2

There is a set point/norm level for each condition
determined by a control center, deviations from the set point are corrected and the set point is restored, a change produces a second change which restores the first change- this is NEGATIVE FEEDBACK. it uses a detector/receptor then a coordinator then an effector to restore optimum

Question 3

Positive feedback

Answer 3

Deviations from the set point, changes are amplified and conditions move further away from original/norm/optimum - an effector increases the change e.g platelets, secreting signals attracting more platelets, pregnancy contractions stimulate more oxytocin stimulating more contractions

Question 4

Name to two functions of the kidney

Answer 4

1. NITROGENOUS excretion (urea removal)

2. OSMOregulation (water regulation)

Question 5

Explain the process of nitrogenous excretion

Answer 5

amino acids cannot be stored, so surplus amino acids are DEAMINATED occurring in the liver:

1. from amino acids, amine group is removed
2. the removed amine group is converted to ammonia
3. with addition of co2, less toxic urea is formed and transported in the blood plasma to the kidneys
4. urea is removed by the kidneys and excreted in the urine

Question 6

Osmoregulation definition and water loss and gain

Answer 6

the control of water content and solute composition of bodily fluids e.g blood, tissue fluid, lymph, also controlling excretion (the elimination of waste products of metabolism from an organism)
- its the homeostatic balance between water gain (food, drink, respiration) and loss ( urination, egestion, sweating, exhalation)

Question 7

Name the components of the urinary system in sequence (5)

Answer 7

1. kidney x2
2. ureter x2
3. bladder
4. sphincter (under conscious control)
5. urethra x1

Question 8

Structure of the kidney

*see unlabeled diagram to name structures (7)

Answer 8

main big tube - ureter
two tubes, smaller lumen with arrow into - renal artery
larger lumen with arrow out - renal vein
middle section - renal pelvis
protective layer surrounding - capsule
outer section with dense capillary network - cortex
inner bubble sections - medulla

Question 9

Location of nephrons and loop of Henle

Answer 9

most of nephrons in the cortex with medulla containing its loop of Henle

Question 10

Structures within the nephron

Answer 10

round ball - BOWMAN’S CAPSULE within is GLOMERULUS
arriving tube - AFFERENT arterioles
exiting tube - EFFERENT arterioles
tube leading to descending limb - PROXIMAL convoluted tubule
tube following ascending limb - DISTAL CT
branched tube - COLLECTING DUCT
descending and ascending limb - LOOP OF HENLE
capillary network - VESA RECTA

Question 11

Explain ultrafiltration

Answer 11

• filtration under high pressure that separates small soluble molecules from blood plasma.
• the small molecules (water, glucose, urea and salts) are filtered from the glomerulus to form a filtrate in the bowman’s capsule.
• high hydrostatic pressure is generated in the glomerulus because the afferent arteriole diameter is wider then the efferent arteriole

Question 12

Ultrafiltration prosses

Answer 12

1. due to high pressure, the fluid containing water and small soluble molecules is forced out of the blood in the capillaries into the pores in the capillary walls, then through the pores in the basement membrane
2. the basement membrane acts as a molecular sieve, allowing small molecules to pass through e.g glucose, salts, urea, water but preventing large molecules and cells from passing through e.g plasma proteins and RBCs
3. the small soluble molecules are then filtered through the feet of the podocytes (aka filtration slits) and glomerular filtrate is formed in the bowman’s capsule

Question 13

Where does selective reabsorption occur?

Answer 13

proximal convoluted tubule (PCT)

Question 14

Selective reabsorption definition

Answer 14

is the process by which useful products , such as glucose and salts, are reabsorbed back into the blood as the filtrate flows along the nephron
the filtrate at the end of the PCT is isotonic to blood plasma

Question 15

What products are selectively reabsorbed, and through what transport mechanism?

Answer 15

• ALL of glucose and amino acids = SECONDARY active transport using co transport with na+
• MOST of mineral ions = ACTIVE transport or CO transport
• MOST of water = OSMOSIS down a water potential gradient
• SOME filtered proteins and urea = DIFFUSION

Question 16

Adaptations of PCT for selective reabsorption (4)

Answer 16

• LARGE SA; due to length and number
• MICROVILLI; on cuboidal epithelial cells to provide large SA and basal channels (absorption wall)
• MANY MITOCHONDRIA; provide ATP for active transport
• TIGHT JUNCTIONS; prevent escaping of reabsorbed materials back into the filtrate

Question 17

Loop of Henle function

Answer 17

The loops of Henle concentrate salts in the tissue fluid of the medulla and that causes an osmotic flow of water out of the collecting ducts and distal convoluted tubules. (preventing water loss in urine)

this water can be reabsorbed into the blood stream via the capillaries of the vasa recta.

this concentrates the urine and makes it hypertonic to the blood (flows out of blood)

Question 18

What are the loop of henle limbs?

Answer 18

the descending limb (1st part) is permeable to water while the ascending limb (2nd part) impermeable to water

Question 19

Loop of henle process

Answer 19

-actively pumping Na+ and Cl- out of the filtrate in the
ascending limb into the tissue fluid creating a low water potential

-the low water potential of the tissue fluid means that
water leaves the descending limb by osmosis and is
carried away by the vasa recta

-the filtrate of the descending limb becoming more
concentrated as they reach the tip (curve end) of the loop of Henle due to the loss of water

• as the filtrate passes up the ascending limb it becomes more dilute due to loss of ions
• an osmotic gradient is maintained down to the tip of the loop of Henlé
• this is called a hair-pin counter-current multiplier

Question 20

ADH: type of feedback? control centre? secreted? role?

Answer 20

ADH secretion has a role in NEGATIVE feedback restoring the normal osmotic concentration in the blood.

OSMORECEPTORS in the HYPOTHALAMUS detect the concentration of the blood plasma.

The hypothalamus secretes ADH which is stored in the
posterior lobe of the pituitary (posterior pituitary gland)
If the blood plasma concentration is too high (lack of water in blood), ADH is secreted and increases the permeability of the distal convoluted tubules and collecting ducts of kidneys to water enabling more concentrated urine to be formed, less water loss

Question 21

What does ADH stand for?

Answer 21

AntiDiuretic Hormone

anti dehydration, reduces water loss in urine

Question 22

Process of ADH forming concentrated urine

Answer 22

ADH enables more concentrated urine to be formed:

• ADH makes the cell membranes of the distal
convoluted tubule cells and collecting duct cells
more permeable to water;
• ADH causes aquaporins to become incorporated in
the plasma membranes, from within the cytosol/cytoplasm;
• water is reabsorbed via vesa recta, by osmosis, from the filtrate into the surrounding, hypertonic, tissue fluid around the DCTs and collecting ducts;
• the urine reaching the bottom of the collecting ducts
has a concentration close to the concentration of
the tissue fluid near the bottom of the loop, that is,
hypertonic to the general body fluids (flows out)

Question 23

Explain the effects of kidney failure and its potential

treatments

Answer 23

effects: kidney filtration is not optimal; blood in urine, water retention (swelling ankles), fatigue

treatments can be used to balance the fluids in blood in the case of kidney failure.
These include: medication to control blood potassium and calcium levels; a lower protein diet;
drugs to reduce blood pressure; dialysis and kidney
transplant