Our external environment

Our internal environment

Homeostasis

• HOMEOSTASIS means maintaining a constant, unchanging internal environment for our cells.

• What are some ways the human body maintains this constant internal environment?

The Urinary SystemStructure and Function

Learning Outcomes:

C13 – analyze the functional interrelationships of the structures of the urinary system

• Identify organs of the urinary system and their functions

• Identify parts of the kidney

• Describe the structure of the nephron

Excretion

• Excretion refers to the removal of metabolic (cellular) wastes from the body

• Organs of excretion include the lungs, liver, skin and kidneys

Fig. 16A

Fig. 16.1

Functions of the Kidneys

• Removal of nitrogenous metabolic wastes such as urea, uric acid, creatinine from the blood

• Maintenance of water and salt balance in the blood (affects blood pressure)

• Maintenance of blood pH by excreting or reabsorbing ions

Nitrogenous Wastes

• When amino acids are metabolized by the liver, the amino group is removed

• This produces ammonia, which is toxic to cells

Urea

• Ammonia combines with carbon dioxide to form urea, which is less toxic and can be safely transported in the blood

• Urea and other nitrogenous wastes are removed from the blood by the kidneys

• All of the blood in the body passes through the kidneys more than 20 times a day

Kidney Structure

• 3 major areas:– Renal cortex -

granulated outer layer

– Renal medulla - striated middle layer

– Renal pelvis - inner cavity

Fig. 16.3

Nephrons

• Structural unit of the kidneys

• Tubule surrounded by capillary network

• Microscopic ~ 106

nephrons per kidney

• In renal cortex and medulla

Nephron Structure

• Bowman’s capsule (glomerular capsule) in the cortex - contains a bundle of capillaries called the glomerulus

• Proximal convoluted tubule - in the cortex nearest to the capsule

• Loop of Henle (loop of the nephron) - extends from the cortex into the medulla

• Distal convoluted tubule - in the cortex

• Collecting duct - extends into the medulla

• Empties into the renal pelvis

Blood vessels

• Renal artery enters the kidney,

• Renal vein takes blood away from the kidney after it has been processed

• Afferent arteriole goes into the capsule

• Glomerulus is a bundle of capillaries inside the capsule

• Efferent arteriole comes out of the capsule

• Peritubular capillary network follows the nephron and surrounds it, allowing for exchange of substances

Fig. 16.4