chapter 11: excretion in humans

Question 1

What are catabolic reactions?
and example

Answer 1

• chemical reaction in which complex substances are broken down into simpler ones
• eg. Glucose ( complex) is oxidases or broken down into carbon dioxide and water (simple) with the release of energy during cellular respiration

Question 2

What are anabolic reactions?

Answer 2

• chemical reactions in which simple substances are built into more complex substances
• eg. The formation of proteins from amino acids

Question 3

What is excretion ?

Answer 3

The process by which metabolic waste products and toxic substances are removed from the body of an organism

Metabolic waste produc s and toxic substances
> excretory products
- most unicellular organisms such as amoeba are able to excrete their waste products by diffusion into the surrounding env
- larger organisms, especially animals with impermeable skin, need special excretory organs

Question 4

What is the structure and the function of the urethra?
(urinary system)

Answer 4

• it’s is the duct through which urine passes from the bladder to the outside of the body

Question 5

What is the function of the sphincter muscle?
(urinary system)

Answer 5

• it is located at the bottom of the bladder
  > used to control urination
• when the bladder is full, sensory neurones send nerve impulses to the brain
  -to urinate, brain sends nerve impulses to the sphincter muscle to cause it to relax
• urine is then able to flow into the urethra and out of the body

Question 6

What is the structure and the function of the urinary bladder?
(urinary system)

Answer 6

• the urinary bladder is an elastic muscular bag located in front of the rectum
  > stores urine

Question 7

What is the structure and function of the ureter?
(urinary system)

Answer 7

• a narrow tube that connects the kidney to the urinary bladder
• urine from each kidney passes through the ureter to the urinary bladder

Question 8

What is the hilus?
(urinary system)

Answer 8

• the surface of the kidney that faces the vertebral column is concave
• at the centre of this concave surface is a depression called the hilus
• the renal artery and the renal vein and the nerves are connected to the kidney at the hilus

Question 9

( structure of kidney)
What is the cortex?

Answer 9

• the outer red region
• it is covered and protected by a fibrous capsule

Question 10

( structure of kidney)
What is the medulla?

Answer 10

• the medulla is the inner pale red region
• the renal pyramids are located in this region

Question 11

( structure of kidney)
What is the structure and function of renal pyramid?

Answer 11

• renal pyramids are conical structures located in the medulla
• the human kidney contains 12-16 pyramids
• the radial stripes on the medulla pyramids indicate numerous kidney tubules
  > nephrons
• urine is formed in the nephrons

Question 12

( structure of kidney)
What is the renal pelvis?

Answer 12

• the renal pyramids project into a funnel like space called the renal pelvis
• the renal pelvis is the enlarged portion of the ureter inside the kidney

Question 13

( structure of a nephron)
what is the bowmans capsule?

Answer 13

• nephron begins in the cortex
  > as a cup-like structure called the bowman’s capsule

Question 14

( structure of a nephron)
what is the proximal convoluted tubule?

Answer 14

• capsule leads into a short, convoluted tubule
  > ( straightens out as it passes into the medulla)\
• the convoluted part is the PCT

Question 15

( structure of a nephron)
what is the loop of Henle?

Answer 15

• in the medulla, the tubule extends into the renal pyramid and makes a uturn back into the cortex
• u-shaped portion

Question 16

( structure of a nephron)
what is the distal convoluted tubule?

Answer 16

• when the tubule enters the cortex again

Question 17

( structure of a nephron)
what is the collecting duct?

Answer 17

• the tubule opens into the collecting duct
  > runs straight through the medulla and eventually opens into the renal pelvis

Question 18

describe blood entering the kidney

Answer 18

-blood enters the kidney by the renal artery which branches out into arterioles
-arterioles further branches into a mass of blood capillaries in the bowman’s capsule (glomerulus)
- the bowman’s capsule with the glomerulus is called the renal corpuscle
- blood leaving the glomerulus enters blood capillaries surrounding the nephron
- blood capillaries unite to form venules which in turn join to form a branch of renal vein

Question 19

describe the process of ultrafiltration

Answer 19

• blood flows from the branches of renal artery into the glomeruli in the renal corpuscles
  > most blood plasma is force out of the glomerular blood capillaries into the bowman’s capsule
• caused by the high hydrostatic blood pressure
  > the AFFERENT arteriole that brings blood into the glomerulus is wider (diameter) than the EFFERENT arteriole which carries blood away
• this creates a high blood pressure in the glomerulus which provides the main force required for the filtration process
• the PPM that wraps the glomerular blood capillaries is a very fine filter
  > BASEMENT MEMBRANE
  > has very small pores that allow only water and very small molecules to pass through

Question 20

describe selective reabsorption.

Answer 20

1. at the PROXIMAL CONVOLUTED TUBULE
   > most mineral salts and all glucose and amino acids (in a healthy person) are adsorbed through the walls of the tubule into the surrounding the blood capillaries
   - solutes absorbed via diffusion and active transport
   > reabsorption is highly selective
   > only absorb substances required by the body
   - most of the water is also absorbed by osmosis here
2. LOOP OF HENLE
   > some water is reabsorbed
3. DISTAL CONVOLUTED TUBULE
   > some water and mineral salts are absorbed
4. THE COLLECTING DUCT
   > some water is reabsorbed
   > excess water, excess salts and metabolic waster products: ( urea, uric acid and creatine) pass out of the collecting duct into the renal pelvis as a mixture called urine

Question 21

( composition of urine)
what will a protein rich diet affect the urine produced?

Answer 21

• more urea present in the urine
  > urea is formed when excess amino acids are deaminated

Question 22

just read :)
a patient with diabetes excretes large amount of glucose in their urine
- they are unable to store up excess glucose as glycogen
> high concentration of glucose in the blood
> glucose is filtered of the glomerulus to form part of the glomerular filtrate
> nephrons are unable to reabsorb all the glucose fast enough
> large amount of glucose in urine

Answer 22

focus on studying. i know its hard but believe me, its going to be worth it :)

Question 23

what is the definition of osmoregulation?

Answer 23

the control of water and solute concentrations in the blood to maintain a constant water potential in the body

Question 24

what is osmoregulation and what is it controlled by?

Answer 24

• water potential of the blood in the body has to be kept constant
  > drastic changes in the water potential of the blood can result in serious problems

eg. when the blood plasma is too diluted
> water enters blood cells by osmosis
> blood cell will swell and burst
- tissue cells will also swell

eg. when the blood plasma is too concentrated,
> water moves out the cells by osmosis
> blood cells and tissue cells will become dehydrated and shrink
> make them unable to carry out their metabolic functions properly > may be fatal

• water potential of the blood depends on the amount of water and mineral salts in the blood plasma
• the amount of water is controlled by antidiuretic hormones (ADH)
  >produced by the HYPOTHALAMUS (region of the brain)
  > released by the PITUITARY GLANDS
  > increases the water reabsorption at the nephrons

Question 25

(osmoregulation)
what happens when there is a loss of water from the body?

Answer 25

• the water potential in blood decreases
  > stimulates the hypothalamus in the brain
  > the pituitary gland releases more ADH into the bloodstream
• cells in the walls of the collecting ducts become more permeable to water
  > more water reabsorbed from the collecting duct into the blood capillaries
• smaller amount od urine is produced
  > urine is more concentrated
  > water potential of blood returns to normal

Question 26

(osmoregulation)
what happens when there is a large intake of water?

Answer 26

• the water potential in blood increases
  > stimulates the hypothalamus in the brain to release less ADH into bloodstream
• cells in the walls of collecting duct become less permeable to water
  > less water reabsorbed from collecting duct into capillaries
• larger volume of urine produced
  > urine produced more diluted
  > water potential of blood returns to normal

Question 27

how does water potential of blood relate to blood pressure?

Answer 27

• the amount of water reabsorbed affects the blood volume
  >which affects the blood pressure
• the higher the blood volume, the higher the blood pressure

Question 28

how do doctors prevent people from having a stroke because of high blood pressure?

Answer 28

• prescribe drugs called diuretics
  > reduce the production of ADH
• a large amount of dilute urine is produced and the volume of water in the blood is decreased
  > lowering the blood pressure

Question 29

what are the common causes of kidney failure?

Answer 29

• high blood pressure
  -diabetes
• alcohol abuse
• severe accidents that physically damage the kidney
• complications from undergoing major surgery

Question 30

what happens when the kidneys fail?

Answer 30

• if one fails > still can lead normal life
• if both fails, person will die unless prompt medical treatment is given
• a person with kidney failure can get a kidney transplant
  -if donor kidney not available, they can be treated with dialysis using a dialysis machine
  > dialysis machine mimics the function of a kidney
  > cleans the patients blood from metabolic waste and toxins
• for effective treatment,
  patient needs to undergo dialysis 2-3 times a wweek
• each session is about 3-5 hours

Question 31

how does a dialysis machine work?

Answer 31

1. blood is drawn from the vein in patient’s arm
   > and is pumped through the tubing in the dialysis machine
2. tubing is bathed in a specially controlled dialysis fluid
   - walls of the tubing in the machine is partially permeable
3. small molecules like urea and other metabolic waste products, diffuse out of the tubing into the dialysis fluid
   > blood cells, platelets and large molecules remain in the tubing
4. the filtered blood is then returned to a vein in the patient’s arm

Question 32

(features of a dialysis machine)
why does the dialysis fluid have the same concentration of essential substances as healthy blood?

Answer 32

• ensures that essential substances (glucose, amino acids and mineral salts)
  > do not diffuse out of the blood into the dialysis fluid
  > + is patients blood lacks these essential substances
  > they will diffuse from the fluid into the blood

Question 33

(features of a dialysis machine)
why does the fluid not contain metabolic waste products?

Answer 33

• this sets up a concentration gradient that allows waste products
  >(urea, uric acid, creatine, and excess water and mineral salts)
  > to diffuse out of the tubing into the dialysis fluid
  >waste products removed from the blood
  > maintains the correct solute composition and water potential of the blood

Question 34

(features of a dialysis machine)
why does the tubing have to be narrow long and coiled?

Answer 34

• increases SA/V ratio which helps speed up the rate of exchange of substances between the patient’s blood and the dialysis fluid

Question 35

(features of a dialysis machine)
why is the direction of the blood flow opposite to the flow of the dialysis fluid?

Answer 35

• maintains a concentration gradient for the removal of waste products