the excretory system

Question 1

what is the main function of the excretory system

Answer 1

To remove toxic metabolic wastes and maintain homeostasis.

Question 2

What are the main organs of the human excretory system?

Answer 2

Kidneys, ureters, urinary bladder, and urethra.

Question 3

What are the key processes carried out by the nephron?

Answer 3

Filtration, reabsorption, secretion, and excretion.

Question 4

what are the waste excretion methods for different organisms

Answer 4

• unicellular organisms (eg microbes) - simple diffusion across plasma membrane.
• simple organisms (eg sponges) - diffusion also method for excretion
• mammals excretion more complex - e.g nitrogenous waste removal by the kidney (uninary system) in the form of urea.
• birds - uric acid
• fish - ammonia

Question 4

Where does filtration occur, and what is the result?

Answer 4

In Bowman’s capsule; produces filtrate from blood plasma.

Question 5

what are sources of nitrogenous waste

Answer 5

• proteins in food broken down into amino acids
• excess amino acids (can’t be stored) and are broken down in liver (deaminntion) into ammonia (NH3) and a carbon skeleton that can be used as a source of energy
• the ammonia is then broken down in the liver into urea and removed in urine.
• the breakdown of nucleic acids into their nucleotide subunits
• metabolic activity of skeletal muscle - generates creatine and it’s derivative, creatinine

Question 5

what is a kidney’s structure

Answer 5

• capsule - thin layer of cells surrounding kidney
• cortex - outmost tissues of kidney that contains nephrons
• medulla - second striated layer - tubes carrying filtered waste to centre of kidney (site of loop of henle)

Question 6

amino acids to urea

Answer 6

excess amino acids + water —(liver)–> ammonia + carbon skeleton (energy production)

Question 6

kidneys and their functions

Answer 6

there are 2 kidneys in the body
1. filters nitrogenous wastes (N wastes) from the blood.
2. remove excess fluid from the body to maintain the normal water balance
3. normal balance of electrolytes in the blood - particularly sodium and potassium
4. maintain blood ph
5. produces renal hormones, e.g. calcitrial - increases calcium levels in the blood and erythropoietin - controls the production of red blood cells.

Question 7

what is the nephron

Answer 7

functional or working unit of the kidney
the nephron is a basic functional unit of kidneys - it helps with filtration and reabsorption
* 200000 to 2 million in the body
* regulation of body fluids within narrow limits
* blood from body flows into tight clusters of capillaries known as glomerulus in each nephron.
the main processes that take place in the nephrons
* ultrafiltration - of blood plasma from the glomerulus, into the bowman’s capsule.
* selective reabsorbtion - from the nephron back into the blood capillaries around them.

Question 7

what is the glomerulus and bowman’s capsule

Answer 7

• the bowman’s capsule forms a thin walled container around the glomerulus - where blood enters the tubule.
• the other end of the tubule connects to the collecting duct to carry filtrate to the ureter.
  1. the mixture of small molecules is called the ultrafiltrate
  2. ultrafilfrate contains; mainly water, with dissolved amino acids, glucose, mineral salts and urea.
  3. red blood cells and large molecules, such as proteins, remain in the blood.

Question 7

what is the loop of henle

Answer 7

• the loop of henle are the section of the nephron tubules that extend in a u-shape into the medulla giving it into the medulla giving it a striated appearance.
  
  • increase the salt contents of the tissues of the medulla
  • this helps in the reabsorbtion of water from the ultrafiltrate in the distal tubules and collecting ducts

Question 8

what are peritubular capillaries

Answer 8

• arterioles leaving the glomerulus form an additional capilliary network around the tubules
• here the exchange of materials between the bloodstream and filtrate in the tubules take place - reabsorbation and secretion

Question 8

what type of transport does reabsorption need?

Answer 8

reabsorption involves active transport of ions and organic molecules such as glucose.
* water moves via passive diffusion created by change in the concertation gradient from movement of the ions.

Question 8

what is the peritubular capillaries

Question 9

formation of urine - hypertonic or hypotonic?

Answer 9

1. hypertonic (mammals) - higher concertation of solutes than present in the body.
2. hypotonic (freshwater fish and amphibians) - lower concertation of solutes (salts) than body fluid of the organism

Question 9

what is ultrafiltration and it’s steps

Answer 9

• filtration is a process which separates particles of different sizes.
• ultrafiltration - when particles being separated are very small, e.g. molecules or ions.
  1. blood in glomerulus is under high blood pressure, like all capillaries, the walls of the glomerulus have pores.
  2. membrane lining bowman’s capsule also has pores. The pressure inside the glomerulus forces small particles from the blood into the bowman’s capsule.

Question 10

what is selective reabsorption

Answer 10

• all substances that are in the ultrafiltrate in bowman’s capsule could pass through the nephron in collecting ducts leading to the renal pelvis.

Question 11

what is the proximal convoluted tubule

Answer 11

• the cells lining this part of the tubule absorb substances from the ultrafiltrate and pass them back into the blood stream, via the capilliaries surrounding the tubules.
• 70% of the water, all of the glucose, some salts and some amino acids reabsorbed.

Question 12

what is the distal tubule and collecting duct

Answer 12

• these are also surrounded bya network of capillaries
• cells in the tubule can absorb materials from the ultrafiltrate and pass them into the blood capillaries
• the cells lining this tubule absorbs mineral salts from the ultrafiltrate and pass them back into the capillary.
• but major function of the distal tubule and collecting duct is to reabsorb water
• amount of water reabsorbed depends on the amount of water in the blood.

Question 13

what is water absorbation, secretion and excretion

Answer 13

• if the blood is dilute - e.g. after drinking large amounts of fluids, less is reabsorbed from the ultrafiltrate, resulting in a greater quantity of dilute urine.
• if blood is too concertrated, e.g. after sweating or eating large amounts of salty food, more water is reabsorbed, resulting in a lesser quantity of more concertrated urine.
  secretion
• excess ions and chemicals such as drugs are secreted from the surrounding capillaries into the tubule with the urine (opposite of reabsorbation).
• these substances are too large to pass through the pores in the Bowman’s capsule at the start of the filtration process.
  excretion
  1. excess water and solutes are eliminated in the form of urine

Question 14

when the kidney’s function fails?

Answer 14

• blood in urine, can be indicative of tumours, kidney stones or an infection.
• protein in urine, tumors, kidney stones or an infection
• glucose in urine, diabetes is the most common cause of elevated glucose levels or may also be a result of renal glycosuria
• dark-coloured urine, most commonly due to dehydration
• frequent urination, can be a sign of urinary problems (habits, pregnancy, diabetes, bladder)