The Urinary System

Question 1

1- describe the anatomical position of the kidneys, bladder, ureter and urethra

Answer 1

Kidneys-
Lie on the posterior abdominal wall, one on each side of the vertebral column
Below the diaphragm
Extend from level of 12th thoracic vertebrae to 3rd lumbar vertebrae
Receive some protection from the lower rib cage
Right kid,yea slightly lower due to space taken by the liver
11cm x 6cm x 3cm
Weighs about 150g
Held in position by a mass of fat

Bladder-
Triangle shaped hollow organ in the lower abdomen
Sits on the pelvic floor
Just posterior to the pubic symphysis

Ureters-
The ureters begin at the junction of the kidneys
Travel inferiorly (low) inside the abdominal cavity
Enter the bladder posteriorly

Urethra-
Passageway located in the body’s pelvic region

Question 2

1- where do blood and lymph vessels in the renal system enter and leave?

Answer 2

Renal blood and lymph vessels enter and leave the kidneys via the HILUM
(This is the same as the nerves and ureters)
The hiking is on the concave medial border of the kidneys

Question 3

1- where is urine formed? Where does it pass after this?

Answer 3

Urine is firmed in the kidneys
Passes through one of several openings in a renal papilla
Goes into the drainage system beginning at minor calyx
Several minor calyces merge into one major calyx
Several major calyces merge to form one renal pelvis (funnel shaped structure that leaves the kidneys)

Question 4

1- what are the walls of the calyces and renal pelvis lined with?

Answer 4

Transitional epithelium (smooth muscle)

Question 5

1- what is peristalsis and its function?

Answer 5

Peristalsis= contraction of smooth muscle
It propels urine through… calyces to renal pelvis to ureters to bladder

Question 6

1- how is the blood supplied to the kidney?

Answer 6

Renal artery

Question 7

1- what does venous drainage go through in the renal system?

Answer 7

Renal vein

Question 8

1- on a microscopic level, what do we study in the kidneys?

Answer 8

Nephrons

Question 9

1- what is a nephron?

Answer 9

A microscopic filtering unit
The kidney is made up of about 1-2 million of these

Question 10

1- describe the structure of a nephron

Answer 10

Each nephron is a tubule that closes at one end and opens at the other end into a collecting duct
Closed end-
forms the cup-shaped glomerular capsule (bowman’s capsule)
The bowman’s capsule encloses the glomerulus, a coil of capillaries
Open end-
In three parts- proximal convoluted tubule, loop of henle, distal convoluted tubule into collecting duct

Question 11

1- describe the function of a nephron

Answer 11

Uses four mechanisms to convert BLOOD TO URINE
1- filtration
2- reabsorption
3- secretion
4- excretion

Question 12

2- name the key parts of the bladder

Answer 12

Peritoneum- covers superior surface of bladder
Bladder wall- has three layers (outer connective tissue, middle smooth muscle, inner mucosa)
Rugae- when empty
Trigone- where three orifices on bladder wall form a triangle (upper two ureters, lower urethral orifice)
Internal urethral sphincter- upper part if urethra to control flow of urine

Question 13

3- name as many parts of the kidney as you can

Answer 13

Hilum
Renal artery
Renal vein
Ureter
Renal pelvis
Major calyx
Minor calyx
Renal cortex
Renal medulla
Renal papilla
Renal pyramids renal columns
Fibrous capsules

Question 14

3- where is the cortex located on the kidney?

Answer 14

Outer layer if the kidney

Question 15

3- where is the medulla located on the kidney?

Answer 15

The inner part of the kidney

Question 16

3- where is the pelvis located on the kidney?

Answer 16

Area at the centre of the kidney where urine collects

Question 17

3- where are the calyces and pyramids located on the kidney?

Answer 17

Calyces-
The outer edges of the kidneys
Where urine collection begins
Each kidney has about 6-10
Several minor calyces merge to form a major calyces which merge to form the renal pelvis

Pyramids-
Within the medulla
Kidney tissues that are shaped like cones

Question 18

4- name as many parts of the nephron as you can

Answer 18

Bowman’s capsule
Glomerulus
Afferent arteriole
Efferent arteriole
Proximal convoluted tubule
Loop of henle
Distal convoluted tubule
Collecting tubule/duct

Question 19

4- where on the nephron is the bowman’s capsule?

Answer 19

Renal cortex part of the kidney (outer)
It encapsulates the glomerulus

Question 20

4- where on the nephron is the glomerus?

Answer 20

Renal cortex part if the kidney (outer)
It is encapsulated by the bowman’s capsule

Question 21

4- where on the nephron is the afferent arteriole?

Answer 21

Renal cortex part if the kidney (outer)
Blood entering the glomerulus

Question 22

4- where on the nephron is the efferent arteriole?

Answer 22

Renal cortex part if the kidney (outer)
Blood leaving the glomerulus

Question 23

4- where on the nephron is the proximal convoluted tubule?

Answer 23

Renal cortex part of the kidney (outer)
Flow of filtrate just before it enters the renal medulla area

Question 24

4- where on the nephron is the loop of henle?

Answer 24

Deep in the renal medulla part if the kidney (inner)
Carries filtrate

Question 25

4- where on the nephron is the distal convoluted tubule?

Answer 25

Renal cortex part if the kidney (outer)
Carries filtrate as it has passed the loop of henle, before it goes back in to medulla and reaches the collecting duct

Question 26

4- where on the nephron is the collecting tubule (collecting duct)?

Answer 26

Renal medulla part of the kidney (inner)
It is the final stage that the filtrate passes through within the nephron

Question 27

4- describe the blood flow through the nephron

Answer 27

Blood enters the kidney at the hilum
Renal artery divides into smaller arteries and arterioles
We then enter the cortex where one tiny arteriole (afferent) enters glomerular capsule
Glomerular capsule divides into a bundle of tiny coiled capillaries- the glomerulus
Between these capillaries are phagocytic cells- protect kidneys from microorganisms
Blood leaves glomerulus via arteriole (efferent- smaller diameter than afferent where blood enters)
Smaller diameter= increased blood pressure in the capillaries, drives the filtration outside the walls
Fluid that has left the blood and entered glomerular capsule= the filtrate!

Question 28

4- describe blood flow round the nephron

Answer 28

The efferent arteriole (where blood leaves the glomerulus) then divides as it enters the renal medulla (inner) area of the kidney
The network that it divides into is called the ‘peritubular capillary network’
This means ‘around’- the capillaries wrap around the remainder of the nephron where the filtrate is flowing
Function of the wrapping- exchange of substances between filtrate and blood…
- supplies tissues with oxygen and nutrients
- removes waste

Question 29

5- describe the formation of urine

Answer 29

The composition of the urine that we see excreted from the urethra is a result of the exchange of blood and filtrate within the nephron and it’s surrounding capillaries
It involves three processes:
-filtration
-reabsorption
-secretion

Question 30

5- describe the physiological process of filtration (with reference to the nephron)

Answer 30

Blood to nephron

Location- The glomerular capsule and glomerulus
These two structures of the nephron have semipermeable walls
Water easily passes through
Fluid is filtered from the blood (in the capillaries of the glomerulus) into the glomerular capsule where it becomes filtrate
Filtrate is very similar to plasma

How is this process possible?
-Difference between blood pressure (in glomerulus) and filtrate pressure (in glomerular capsule)
-Efferent arteriole (blood leaves) is narrower than the afferent arteriole (blood enters)= hydrostatic pressure

Question 31

5- describe the physiological process of reabsorption (with reference to the nephron)

Answer 31

Filtrate to blood

There are two types of reabsorption: selective and active

Many substances reabsorbed: water, electrolytes, glucose, amino acids…
Takes place in proximal convoluted tubule of the nephron
Epithelial lining containing microvilli increases SA for absorption
Only 60-70% of filtrate reaches medullary loop (loop after the glomerulus)
Even more reabsorption takes place when that filtrate manages to reach the loop
Only 15-20% filtrate reaches distal convoluted tubule (upper loop before collecting duct)
More electrolytes reabsorbed in convoluted tubule
Filtrate reaches collecting duct and is very dilute

Four hormones influence reabsorption:
-Parathyroid hormone- regulates calcium and phosphate reabsorption for blood level stabilisation
-Antidiuretic hormone (ADH)- increases permeability of tubules and collecting ducts. Osmoreceptors in the hypothalamus monitor water content if blood and adjust ADH secretion accordingly
-Aldosterone- increases reabsorption of sodium and water
-Atrial Natriuretic Peptide (ANP)- secreted in response to stretching of atrial walls. Increases urinary volume and decreases blood volume

Question 32

5- describe the physiological process of secretion (with reference to the nephron)

Answer 32

Blood to filtrate

Filtration happens in the glomerulus, but not all substances are entirely filtered out of the blood because it passes through the glomerulus so quickly, or they are too large!
E.g. Penicillin molecules are too big
Since these substances can not be absorbed, they are secreted from blood to filtrate
This happens in peritubular capillaries in convoluted tubules

Secretion of hydrogen (H+) ions is important for blood pH levels

Question 33

6- list the constituents of urine

Answer 33

Water- 96%
Urea- 2%

Remaining 2%…
Sodium, potassium, chlorides, uric acids, ammonia, sulphites, phosphates etc

Question 34

6- describe water balance and urine output

Answer 34

Most body water comes from food and fluid that we ingest
We have a very small amount that does not come from ingestion, instead it occurs as a by-product of cellular metabolism

The main way that we get rid of water is through urine! (96% of urine is water)
We also loose a little bit of water in air, sweat and faeces

We balance the intake and output of water using our kidneys
-we need at least 500ml of water per day for minimum excretion
-anything in excess of 500ml is controlled by ADH (using Osmoreceptors in the hypothalamus)
-increased osmotic pressure= blood becoming more concentrated= increased ADH output
-reabsorption of water in tubules and collecting ducts is increased= reducing osmotic pressure= lowering ADH output again
NEGATIVE FEEDBACK MAINTAINS OSMOTIC HOMEOSTASIS

Question 35

6- describe electrolyte balance and urine output

Answer 35

There is a concentration of electrolytes in body fluids
This may be due to:
-changes in body water content
-electrolyte levels

The concentration can be increased by:
-increasing water content
-increasing the amount of solute it contains

Question 36

6- describe sodium and potassium balance in urine

Answer 36

Sodium- most common extracellular cation (+tive charge ion)
Potassium- most common intracellular cation (+tive charge ion)

How are they excreted?
Sodium- mostly in urine and sweat as tends to exceed body needs due to salt in food
Sodium and potassium- RAAS system maintains both within physiological limits
Sodium and potassium- in digestive juices and absorbed by large intestine

Question 37

6- describe the RAAS system

Answer 37

Renin-Angiotensin-Aldosterone-System

It is a hormone system within the body
It is essential to regulate BP and fluid balance
Three substances: renin (enzyme), angiotensin (hormone), aldosterone (hormone)

What do they do:
Increases sodium reabsorption to regulate BP
Increases water reabsorption to regulate BP
Controls vessel constriction and dilation to regulate BP

Enzymes- trigger chemical reactions
Hormones- coordinate different tissue functions