Homeostasis

Question 1

Excretion Definition

Answer 1

Removal of waste products of metabolism from the body

Question 2

What do kidneys excrete

Answer 2

Nitrogen containing cmonds

Urea - breakdown excess aa and nucleic acids in liver

Creatinine - degradation of creatine phosphate in muscles

Question 3

Homeostasis

Answer 3

Maintenance of steady states within the body

Question 4

Osmoregulation

Answer 4

Control water potential of body fluids - kidneys under influence of Antidiuretic Hormone

Question 5

Structure Urinary System

Answer 5

Question 6

Egestion

Answer 6

Removal from the body of waste material - undigested food- which has not been part of the bodys metabolism

Question 7

How much cardiac output do kidneys receive

Answer 7

25%

Question 8

2 Layers of Kidney

Answer 8

Outer Cortex
Inner Medulla

Question 9

What is the central cavity in a kidney

Answer 9

Pelvis

Question 10

What is structure of medulla

Answer 10

Sub-divided into pyramids - apices protrude into pelvis

Question 11

What do kidneys contain over 1 million of?

Answer 11

Nephrons - microscopic tubules
Each rich blood supply

Functional Unit of the Kidney

Question 13

Structure Nephron

Answer 13

Bowmans Capsule

3 Regions:
Proximal Convoluted Tubule
Loop of Henle
Distal Convoluted Tubule

Question 14

How does blood enter nephron

Answer 14

Arterial blood enters through an afferent arteriole - branches to form capillary network - glomerulus

Question 15

How does blood leave glomerulus

Answer 15

Leaves through efferent arteriole - branches form a further capillary network - vasa recta
- around main body of nephron

Nephrons join to form collecting duct - transfers fluid towards the pelvis

Question 16

2 Stages of Production Urine

Answer 16

Ultrafiltration
Reabsorption

Question 17

Ultrafiltration

Answer 17

Stage in which plasma in glomerulus is filtered into Bowmans Capsule

Only substances below certain size are filtered - filtrate contains useful molecules as well as toxic ones

Question 18

Reabsorption

Answer 18

Useful substances reabsorbed into blood

Occurs as filtrate passes along the nephron and collecting duct

Only at point where collecting duct joins with pelvis can fluid be called “urine”

Question 19

Driving Force Of Ultrafiltration

Answer 19

Hydrostatic Pressure

Occurs because:
•renal arteries wide, short and relatively close to heart
•efferent arteriole is smaller than afferent - creates bottleneck

HP causes fluid to filter from glomerular plasma as filtrate in capsule

Question 20

The Filter of Ultrafiltration

Answer 20

3 layers separating plasma from filtrate
-capillary endothelium
-basement membrane
-inner cell layer Bowmans

Effective filter is Basement Membrane of glom capillaries - extracellular membrane lies on outer side of capillary endothelium

Question 21

Which two layers are especially porous

Answer 21

-endothelium of capillaries - single layer of squamous cells with pores between

-inner wall of Bowmans - consists of podocytes - footlike processes which surround capillaries - spacious gaps between called filtration slits

Question 22

Composition of Filtrate

Answer 22

Only molecules with RMM of less than 68,000 can pass through basement membrane

All constituents of blood plasma -other than plasma proteins (except for smallest) - are able to pass through

Filtrate consists of mainly inorganic ions, glucose, aa, urea and other toxic molecules, all dissolved in water

Clearly, water and useful substances must be reabsorbed

Question 23

Reabsorption in Convoluted Tubule

Answer 23

As filtrate flows through PCT, 80% water reabsorbed by osmosis into adjacent blood capillaries

67% ions reabsorbed - partly by diffusion (following reab of water) and partly by active transport

All Glucose and Amino Acids pass back into blood by active transport

Small proteins reabsorbed by pinocytosis

By end PCT filtrate is isotonic with plasma - same water potential

Question 24

Structure Cuboidal Epithelial Cells in PCT

Answer 24

Line wall

Numerous microvilli on luminal surface
Infoldings of basal cell-surface membrane next to blood capillaries

Adaptions greatly increase SA available for re absorptive processes

Cells have many mitochondria located near infoldings - supply extra ATP needed for Active Transport

Question 25

Other Adaptions to increase Reabsorption Efficiency

Answer 25

Close association of many capillaries Thin squamous endothelium of capillaries Flow of filtrate and blood maintaining conc gradients

Question 27

Reabsorption in PCT

Answer 27

As filtrate flows through PCT - 80% water reabsorbed by **osmosis** into adjacent blood capillaries 67% ions reabsorbed- partly by diffusion (following reab of water) and partly by active transport All Glucose and Amino Acids pass back into blood by active transport Small proteins reabsorbed by **pinocytosis** By end PCT, filtrate is isotonic with the plasma *(same water potential)*

Question 28

Structure Cuboidal Epithelial Cells

Answer 28

Line tubule walls Numerous **microvilli** on luminal surface **Infoldings** of the basal CSM next to blood capillaries Adaptions greatly increase SA available for re absorptive processes Cells have many mitochondria near infoldings - supply extra ATP needed for Active Transport

Question 29

Other Adaptions of PCT cells for reabsorption

Answer 29

Close association of many capillaries Thin squamous endothelium of capillaries Flow of filtrate and blood maintaining conc gradients

Question 30

Role of Loop of Henlé

Answer 30

Na+ and Cl- ions pass out of ascending limb - diffusion and AT - into surrounding tissue of medulla - lowering water potential Creates osmotic gradient - draws water out of permeable descending limb - carried away by blood in surrounding capillaries Ascending limb is impermeable to water Comb of water and ion mvnt causes fluid (in and around loop) to be **saltier** down descending limb - becomes less salty up ascending Tissues deeper in medulla higher conc ions and more negative Wp As collecting ducts pass medulla, water reab by osmosis - more conc urine

Question 31

Reab in DCT

Answer 31

Ionic composition and pH of blood adjusted It is here that toxic substances (creatinine) secreted into filtrate Depending on permeability of tubule walls - some water may be reabsorbed

Question 32

What does longer loop of henle mean

Answer 32

Greater decrease in Wp in medulla More water can be reabsorbed Desert animals have very long

Question 33

How are Cl- ions pumped into medulla

Answer 33

Upper thick region of ascending limb composed of cuboidal cells -rich In mitochondria Provide ATP necessary to pump Cl- ions reabsorbed

Question 34

Osmoregulation

Answer 34

Collecting ducts is where water content of blood is regulated Permeability of DCT and collecting ducts pass incr by **Antidiuretic Hormone**

Question 35

Where is ADH produced and where is it stored

Answer 35

Hypothalamus secreted into posterior lobe of pituitary body - where it is stored

Question 36

Osmoregulation Of Rise in Blood Conc

Answer 36

Wp become more - •Detected by osmoreceptors in hypothalamus •Receptors send impulses to posterior lobe of pituitary gland •lobe of p gland releases **more** ADH into blood - increases perm of DCT and CD •water moves through channel proteins *(aquaporins)* which open to let water through •More water passes to medulla - more conc (**hypertonic**) urine produced

Question 37

Osmoregulation Fall in Blood Conc

Answer 37

Wp blood becomes less - Inhibits release of ADH As result - walls DCT and CD impermeable to water Less water reabsorbed and less conc (**hypotonic**) urine produced

Question 38

Negative Feedback

Answer 38

Feedback since change in Wp of blood will lead to another change in Wp of blood Negative since an incr in Wp will later result ina decr. of Wp