1. The Urinary System

2. Urinary System One of the excretory systems of the body
It consists of the following structures
2 kidneys – secrete urine
2 ureters – convey urine to the bladder
1 urinary bladder – stores urine temporarily
1urethra – conveys urine to the exterior
Functions : homeostasis of water and electrolytes
Metabolic waste products (the nitrogenous compounds like urea, uric acid excess ions and some drugs are excreted
Stimulation of erythropoiesis (erythrocyte prduction)
Control of blood volume
Passing urine is called micturition

3. Kidneys Definition Bean shaped organs which secrete and excrete urine
Situation
On the posterior abdominal wall
One on each side of the vertebral column
Retroperitoneal
Below diaphragm
11 cm x 6 cm x 3 cm
Embedded in and surrounded by a mass of fat called the perirenal fat
Renal fascia = a fibroelastic tissue sheet of tissue encloses the perirenal fat and the kidney

4. Relations
Right Kidney
Superiorly : adrenal gland
Anteriorly : right lobe of liver, duodenum, hepatic flexure of colon
Posteriorly : diaphragm, muscles of the posterior abdominal wall
Left kidney
Anteriorly : the spleen, stomach, pancreas, jejunum splenic flexure of colon
Posteriorly : diaphragm, muscles of the posterior abdominal wall.

5. Structure
Three areas : - fibrous capsule surrounding the kidney
The cortex is the reddish brown layer of tissue immediately under the capsule and between the pyramids
The medulla – innermost layer – pale conical shaped striations the renal pyramids
Hilum – concave medial border where the nerves vessels enter
The pelvis is the funnel shaped structure – receptacle for urine. It has branches called calyces (calyx) – each branch surrounds the apex of a renal pyramid – urine  through a papilla at the apex of a pyramid minor calyx major calyx  renal pelvis

6. Walls of pelvis contains smooth muscle fibres – lined with transitional epithelium
Pacemaker cells in the walls of the calyces – peristaltic movements – started – urine propelled – intrinsic function not controlled by nerves

13. Microscopic Structure of the Kidney
One million functional units called the nephrons
Smaller number of collecting tubules
Transport urine through the pyramids to the pelvis
The tubules give the pyramids the striped appearance

14. The Nephron
Consists of a tubule closed at one end
The other end opens into a collecting tubule
The closed end forms a cup – glomerular capsule (Bowman’s capsule)
Inside a capillary network – glomerulus
Walls of the glomerulus and the glomerular capsule have a single layer of flattened epithelial cells – the remainder of the nephron and the collecting tubule have a single layer of highly specialised cells

15. The remainder of the nephron is 3 cm has three parts:-
The proximal convoluted tubule
The medullary loop (the loop of Henle)
The distal convoluted tubule leading into a collecting tubule

16. Blood Supply Arterial supply Renal artery hilum  arteriole in
In the Cortex an arteriole enters the glomerular capsule – the afferent arteriole
Subdivides into a cluster of capillaries – glomerulus
Between the capillary loops there are connective tissue phagocytic mesangial cells
The arteriole that leaves the glomerulus – the efferent arteriole

17. Outside the glomerulus the efferent arteriole becomes a capillary network and supplies the rest of the nephron
Venous drainage
Ultimately through the renal vein  IVC
Nerve supply
Sympathetic and parasympathetic nerves
Lymphatic drainage
To the paraaortic lymph nodes