The Kidneys LO

Question 1

Identify the organs associated with the kidneys

Answer 1

Right kidney
- superiorly - the right adrenal gland
- anteriorly - the right lobe of the liver, the duodenum and hepatic flexure of the colon
- posteriorly - the diaphragm, and muscles of the posterior abdominal wall
Left kidney
- superiorly - the left adrenal gland
- anteriorly - the spleen, stomach, pancreas, jejunum and splenic flexure of the colon
- posteriorly - the diaphragm, and muscles of the posterior abdominal wall

Question 2

Outline the gross structure of the kidneys

Answer 2

Three different areas of tissue:
- outer fibrous capsule enclosing kidney
- the cortex, reddish-brown layer immediately below capsule and dipping in between the renal pyramids
- the medulla, the innermost layer, consisting of pale, conical-shaped, striated structures, the renal pyramid. Each pyramid has a pointe proximal end called the papilla
- The hilum is the concave medial border of the kidney

Question 3

Describe the structure of a nephron

Answer 3

• tubule that is closed at one end and opens into a collecting duct at the other
• closed end forms cup-shaped glomerular (Bowman’s) capsule which almost encloses capillaries in the glomerulus
• after glomerular capsule: proximal convoluted tubule, medullary loop (loop of henle), distal convoluted tubule, leading to collecting duct

Question 4

Explain the processes involved in the formation of urine

Answer 4

Kidneys form urine and adjust the amounts of other substances excreted
- FILTRATION - takes place through semipermeable walls of glomerular capillaries and glomerular capsule. Water and other small molecules readily pass through although some is reabsorbed later, some molecules are larger and can’t pass through so they remain in the blood.
- SELECTIVE REABSORPTION - most takes place in the proximal convoluted tubule. It’s epithelial lining has microvilli to increase surface area; water, electrolytes and nutrients (glucose and amino acids) are reabsorbed here. Some molecules are reabsorbed passively, others by active transport. Only 60-70% reaches the medullary loop.
- SECRETION - happens as blood flows through the glomerulus. Some unwanted substances may not be entirely filtered out of the blood due to the short time spent passing through the glomerulus or because they are too big to fit through the pores.

Question 5

Explain how body water and electrolyte balance is maintained

Answer 5

WATER BALANCE
- most water comes from ingested food and fluids, small part formed as a byproduct of cellular metabolism, called metabolic water
- water is excreted via urine and sweat
- amount of urine released is controlled by antidiuretic hormone (ADH) from posterior pituitary gland
- sensory nerve cells in hypothalamus respond to changes in osmotic pressure
- impulses from osmoreceptors control release of ADH
- if osmotic pressure is raised > ADH output increased > increased reabsorption via distal convoluted tubule
ELECTROLYTE BALANCE
- change in electrolyte balance may be due to changes in the body’s water content
- concentration of fluid can be increased by reducing the water content or increasing the amount of solute it contains

Question 6

List the substances that pass in or out of the nephron during filtration, reabsorption and secretion

Answer 6

Filtration
- essential ions, glucose, amino acids and smaller proteins
Reabsorption
- Ca2+, Na+, glucose and amino acids
Secretion
- potassium ions, hydrogen ions and some xenobiotics