Urinary system
The main function of the urinary system is to maintain homeostasis by regulating the volume and concentration of body fluids
Where are the kidneys found
- The two kidneys are found in the abdominal cavity below the diaphragm
- they lie next to the posterior wall on either side of the vertebral column
- they are kept in position by being to a thin layer of connective tissue
What do kidneys look like externally
They are beaned shape and dark red in colour.
Each kidney has 3 layers:
1. Renal capsule: covers the kidney, preventing infections from spreading to kidney
2. Fatty tissue: helps hold the kidney in place and cushions it from blows
3. Renal fascia which anchors the kidney to the surrounding structures
Nephrons
Each tubule is made up as follows:
- Renal corpuscle found in the renal cortex made up of:
- Bowman’s capsule
- glomerulus - Renal tubule found in the cortex and medulla and made up of a:
- proximal consulates tubule
- loop of Henle
- distal consulates tubule
How does a kidney function
A. Glomerular filtration
- the fluid part of the blood is filtered from the glomerulus into the cavity of the bowman’s capsule
B. Tubular reabsorption
- as the fluid along the renal tubule, useful substances are reabsorbed back into the bloodstream
C. Tubular excretion
- in addition certain unwanted substances in the blood are actively excreted into the tubules
Glomerular filtration and afferent vs efferent
Takes place in the many renal corpuscles.
Afferent: carry towards
Efferent: carry away from
Glomerular filtration: how is filtration brought about?
Blood enters the glomerulus through the wider afferent arteriole and leaves through the narrower efferent arteriole. More blood will enter than leave. In this way pressure is built up, forcing the filterable content of the blood through the glomerular membrane into the cavity of Bowman’s capsule
Glomerular filtration: how is the glomerular membrane adapted for filtration
The glomerular membrane is made up of two layers of cells:
- The endothelial cells making up the wall of the glomerular capillaries are porous, allowing the plasma through
- Podocyte layer of Bowman’s capsule, made up of flattened cells, podocytes that have spaced between them called filtration slits. These filtration sloit are too small to allow plasma protein molecules.
A very thin basement membrane covers each capillary, so it occurs between these two layers
Glomerular filtration: what makes up the glomerular filtrate
Useful substances: water, glucose, amino acids, vitamins, hormones and ions
Waste substances: nitrogenous waste such as uric acid, urea and creatinine
Glomerular filtration: sum up
It is a passive, non-selective process in which fluids and solutes are forced through the glomerular membrane my hydrostatic pressure
Blood pH regulation
- pH 7 is neutral
- pH 7 down to pH 0 indicates an increase in acidity
- pH 7 up to pH 14, indicates an increase in alkalinity
What is a buffer
Is a chemical substance that prevents too great a change in pH
Formation of urine
The filtrate that flows from the collecting ducts can finally be called urine
What is the final composition of urine
About 96% water, salts make up 1,5%, urea make up 2%, small quantities of uric acid, creatine and ammonium ions also occur
How does urine move out of kidneys
From the collecting ducts the urine:
- passes into the renal calyx and then into the renal pelvis
- it is then propelled along two ureters to the bladder by peristaltic movements of muscular
- it is stored in the bladder until it can be expelled through urethra
How is urine expelled from the bladder
The expulsion of urine from the bladder is called urination
- urination is a flex action that is triggered by filling the bkadder
- impulses from the autonomic nervous system stimulate the bladder muscles to contract and the internal sphincter to relax
- at the same time the external sphincter opens voluntarily so urine can flow out the urethra
