Topic 13 - Excretion

Where urine flows to the bladder

Ureter

Where blood is carried into the kidney

Renal artery

Where blood flows out of the kidney

Renal vein

two waste products removed from the blood by dialysis

Urea and salts

Function of renal capsule in kidney

• ultrafiltration

• High blood pressure pushes out the substances (filtrate) from glomerulus to Bowman’s capsule

• filtrate contains glucose salts water and urea

Define active transport

Movement of substances across membranes from low to high concentration against a concentration gradient using energy from respiration. It uses a carrier protein in the membrane

Explain how dialysis machine filters blood

• has partially permeable membrane . dialysis fluid contains normal level of glucose salt and no urea.

• Urea in the blood diffuses into dialysis fluid along the concentration gradient

• If salt and glucose concentrations are high in blood, they will also diffuse into the dialysis fluid along concentration gradient.

• Protein and blood cells are large so they don’t pass through the membrane

Advantages of a kidney transplant compared with dialysis

• Patients do not need to return to the clinic regularly, less effect of the quality of life.

• No needles in arms

• less risk of getting a blood borne infection transmission.

• Less fluid and diet restrictions

Why is it important to tissue match the donor with the recipient

To avoid tissue rejection

Name the process of maintaining constant conditions of the host

Homeostasis

Which molecules are too large to be filtered

Protein

Molecules small enough to be filtered but is completely reabsorbed in the fluid in the kidney tubule,

Glucose

human excretory system is

a group of organs which are specialised for the removal of certain excretory product

organs involved in the excretory system

lungs, kidney, liver

what do the lungs excrete and why

carbon dioxide (the waste product of aerobic respiration) during exhalation.

what do kidneys excrete and why

excess water, salts and urea (produced in the liver from excess amino acids) through the formation of urine

Excretion is

the removal of the waste substances of metabolic reactions, toxic materials and substances in excess of requirements

metabolic reactions

the chemical reactions that take place inside cells

why must carbon dioxide be excreted

it dissolves in water easily to form an acidic solution which can lower the pH of cells, hence reduce the activity of enzymes in the body which are essential for controlling the rate of metabolic reactions

kidney

Two bean-shaped organs that filter the blood

ureter

Tube connecting the kidney to the bladder

bladder

Organ that stores urine (excess water, salts and urea) as it is produced by the kidney

urethra

Tube that connects the bladder to the exterior; where urine is released

function of kidneys

• regulates water content of blood to maintain blood pressure

• excretes toxic waste products of metabolism and substances in excess of requirements

Each kidney contains around a million tiny structures called

nephrons, also known as kidney tubules or renal tubules

nephron process

1. nephrons start in the cortex of the kidney

2. loop down into the medulla and back up to the cortex

3. contents of the nephrons drain into the innermost part of the kidney and the urine collects there before it flows into the ureter to be carried to the bladder for storage

process of ultrafiltration

• Arterioles branch off the renal artery and lead to each nephron, where they form a knot of capillaries (the glomerulus) sitting inside the Bowman’s capsule

• The capillaries get narrower as they get further into the glomerulus

• which increases the pressure on the blood moving through them (which is already at high pressure because it is coming directly from the renal artery which is connected to the aorta)

• This eventually causes the smaller molecules being carried in the blood to be forced out of the capillaries and into the Bowman’s capsule,

• where they form filtrate

substances forced out during ultrafiltration

glucose, water, urea, salts

Some of these are useful and will be reabsorbed back into the blood further down the nephron

components of filtrate in ultrafiltration

• water

• salts

• glucose

• urea

where is water reabsorbed after ultrafiltration

loop of henle and collecting duct through osmosis

where are salts rebasborbed after ultrafiltration

loop of henle

where is glucose reabsorbed after ultrafiltration

proximal first convoluted through active transport

where is urea reabsorbed after ultrafiltration

not reabsorbed

why is excretion of urea important

Urea is toxic, it can lower the pH of the body and denature the enzyme. Denaturing of enzyme might lead to death of the individual therefore excretion of urea is important.

how is nephron adapted to reabsorbing glucose

having many mitochondria to provide energy for the active transport of glucose molecules

why cant reabsorption of glucose not occur in anywhere else but the proximal first covuluted tube

the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule

Which diet will cause the liver to produce the most urea?

A ) high carbohydrate, low fat

B ) high fat, high fibre

C ) high fat, low protein

D ) high protein, low carbohydrate

D

Where is urea formed?

A) kidneys

B) liver

C ) muscles

D ) small intestine

B

Which substance is lost from the body of a healthy person by the kidneys, but not by the lungs?

A carbon dioxide

B glucose

C urea

D water

C

What is a function of the kidneys of a healthy person?

A break down toxins

B eliminate all salts

C reabsorb all glucose

D retain all water

C

What is the function of the kidney?

A making glucose and reabsorbing urea

B making urea and removing salts

C removing glucose and reabsorbing salts

D removing urea and reabsorbing glucose

D

why are one of the first tests a doctor may do to check if someone is diabetic is to test their urine for the presence of glucose

People with diabetes cannot control their blood glucose levels and they are often very high, meaning that not all of the glucose filtered out can be reabsorbed into the blood in the proximal convoluted tubule

As there is nowhere else for the glucose to be reabsorbed, it continues in the filtrate and ends up in the urine

where is urea formed and from what

formed in the liver from excess amino acids

deamination as

the removal of the nitrogen-containing part of amino acids to form

urea

assimilation

when food molecules are converted to other molecules that the body needs

Many digested food molecules absorbed into the blood in the small intestine are carried to the liver for _____

assimilation

Egestion is

the expulsion of undigested food waste from the anus.

amino acids, which are used to build proteins such as

fibrinogen, a protein found in blood plasma that is important in blood clotting

why happens to excess amino acids absorbed in the blood that are not needed to make proteins

cannot be stored, so they are broken down in deamination

In demanination enzymes in the liver split up the ____1___

The part of the molecule which contains carbon is turned into ____2____ and stored

The other part, which contains nitrogen, is turned into __3___, which is highly toxic, and so is immediately converted into __4__, which is less toxic

The __4_ dissolves in the blood and is taken to the kidney to be excreted

A small amount is also excreted in sweat

1) amino acid molecules

2) glycogen

3) ammonia

4) urea

what happens to the nitrogen-containing amino group in deamination

removed and converted into ammonia and then urea to be excreted

toxic consequences of high urea levels, if it is not excreted effectively, are very serious:

Cell death

Reduced response to insulin, leading to diabetes

Deposits inside blood vessels

Where is blood filtered in kidney?

Cortex

Outline the role of liver in excretion.

Deamination of amino acids, removal of nitrogen-containing part of amino acids to produce urea

urea passes into blood

breakdown of, hormones, toxins, drugs, excess vitamins.

break down of, worn out red blood cells

excretory products put in bile ;

Outline the role of the glomerulus.

provides blood at high pressure

provides a large surface area

ultrafiltration (filters bloods)

large insoluble molecules stay in the glomerulus

soluble particles are moved out

What is the function of collecting duct?

reabsorbs water and passes urine to ureter

Describe the process of blood clotting.

platelets, soluble fibriongen is turned to insolutble fibrin and a mesh is created to trap blood cells

Outline how the kidney tubules function to produce urine from substances in blood plasma.

• no protein in bowman’s capsule

• protein is only in the blood plasma

• all glucose, salts, urea are filtered out of blood plasma and into the Bowman’s capsule

• glucose is reabsorbed in loop of henle

• some salts are reabsorbed by loop of henle in tubule

• urea concentration is higher in loop of henle

• size of substances determines what is filtered (glucose, salts, urea filtered out of blood but proteins are not filtered out)

• active transport of glucoe/salts occurs from the tubule and back into the blood plasma

• glucose and salts move against a concentration gradient through proteins in membranes

• active transport uses energy from respiration in mitochondria

• most water is reabsorbed by osmosis in loop of henle

• urea concentration increases as a result of reabsoption of water

• urea is an excretory substance of metabolism

• urine contains salts and urea

what does urine contain

salts and urea

The renal artery carries blood at high pressure to the kidneys because

pressure is essential for ultrafiltration, where small molecules are forced out of the blood and into the nephrons for filtration and waste removal. renal artery, a branch of the aorta, supplies the kidneys with blood

Explain the importance of the microvilli on the surface of cells.

increases surface area of villi for faster reabsorption of glucose, amino amino acids, minerals, ions, salts, water

Where are amino acids deaminated and converted into urea

• Liver

Explain how, when the patient is receiving dialysis treatment the loss of plasma proteins and red blood cells is prevented,

they are too large to go into the membrane

Explain how, when the patient is receiving dialysis treatment the normal glucose concentration of the blood is maintained

dialysing solution contains glucose. glucose diffuses into the blood until it is at a normal concentration

balanced diet definition

diet that provides sufficient energy, nutrients, and all food groups in correct quantities for metabolism

The urea produced is transported to the kidney, where it is excreted. Describe how urea is transported in the blood to the kidney

it is dissolved in the plasma to be transported

how is glucose reabsorbed

diffusion and active transport

how is water reabsorbed

osmosis

name the liquid part of blood

plasma

State two components of blood that are not in dialysis fluid

• red blood cells

• white blood cells

describe how kidney tubules reabsorb glucose from the filtrate.

by active transport from filtrate against concentration gradient from low to high concentration using energy from respiration

When plants are grown in a solution that includes a poison that prevents respiration, the roots continue to absorb water, but do not absorb many ions. Explain this result

• active transport of ions against concentration gradient into the root

• energy needed comes from respiration

• water is absorbed by osmosis down water potential gradient

• diffusion/osmosis does not require energy, occurs until equilibrium

order of stages in filtration of blood

- blood from renal artery enters the glomerulus

- high pressure forces small substances (glucose, urea, ions, water, amino acids) to enter the bowmans capsule (ultrafiltration)

- Glucose, amino acids, some ions and some water are reabsorbed

- water moves out of loop of henle

- salts move out of the loop of henle

- water moves out of the collecting duct

- urine enters ureter