Kidney Blood Supply

• Each kidney gets its blood supply from a renal artery.
• The renal artery is a branch of the aorta, transporting oxygenated blood loaded with metabolic waste to the kidneys.
• The renal artery enters the kidney at the hilum.
• The artery branches into smaller arteries, extending between the pyramids toward the cortex.
• These further branch into the smallest cortical branches: afferent arterioles.
• One afferent arteriole extends to each Bowman's capsule.
• The afferent arteriole splits into a capillary network, the glomerulus, nestled within the Bowman's capsule.
• These capillaries converge to form an efferent arteriole, carrying blood away from the glomerulus.
• The efferent arteriole branches again into the peritubular capillary network, surrounding the renal tubule.
• Afferent arterioles are wider than efferent arterioles, maintaining high glomerular blood pressure.
• The peritubular capillaries combine into venules and larger veins, forming the renal vein.
• The renal vein carries deoxygenated blood, minus waste, from the kidney to the heart via the inferior vena cava.
• The kidney functioning are divided into three processes: Glomerular filtration, Tubular reabsorption, and Tubular excretion.
• The efferent arteriole has a capillary network on both sides: the glomerulus, and the peritubular capillaries, is called a portal system.

Kidney Structure

• The kidney is encapsulated by a connective tissue membrane, the renal capsule, for protection.
• Directly beneath is the cortex layer.
• The medulla is the lighter-colored, inner region, with grouped tubes.
• Each tube group forms a pyramid, its base faces the cortex.
• The renal papilla is at each pyramid tip.
• Tubes in each renal papilla open into renal calyxes.
• The renal calyxes merge into the ureter region known as the renal pelvis.

Microscopic Internal Structure

• Each kidney is made of about one million nephrons.
• Nephrons are the kidney's structural and functional units.
• 'Structural units' = the building blocks making up the kidney.
• 'Functional units' = independent units performing kidney functions.

Nephron Structure

• Each nephron has two primary parts: the Malpighian body and the renal tubule.
• The Malpighian body, found in the cortex, includes the Bowman's capsule (double-walled, cup-shaped) and the glomerulus (capillary network).
• Glomerular capillaries have single endothelial layer with pores.
• The afferent arteriole transports blood to the glomerulus.
• The efferent arteriole carries blood away from the glomerulus.
• A comes before E - Afferent transports to, Efferent transports away.

Renal Tubule

• The renal tubule, a long and winding tube, lies partly in the cortex and partly in the medulla.
• The tube has three sections: proximal convoluted tubule, loop of Henle, and distal convoluted tubule.
• The proximal convoluted tubule follows the Bowman's capsule and is in the cortex.
• Has a single layer of cuboidal epithelium and is widest, at this part.
• The loop of Henle, situated in the medulla, features a descending limb extending into the medulla, a hairpin loop, and an ascending limb returning to the cortex.
• The distal convoluted tubule is in the cortex, also has a single layer of cuboidal epithelium, receives input from several nephrons' distal tubules.
• Distal convoluted tubules drain into collecting ducts.
• The tubes forming the pyramids and which open into the renal calyx of the renal pelvis, are the ducts of Bellini.

Podocytes

• The Bowman's capsule inner wall has podocytes, specialized cells.
• Podocytes have projections that create filtration slits.
• The cavity between the Bowman's capsule inner and outer walls is the Bowman's capsule cavity.
• The blood in the glomerulus is separated from the Bowman's capsule cavity by: a thin endothelial cell layer with pores & the podocyte layer with filtration slits.

Urinary system in humans

• The urinary system includes two kidneys, two ureters, the bladder, and the urethra.
• Renal arteries and veins are the blood vessels associated with the urinary system.
• Kidneys are in the abdominal cavity, on either side of the vertebral column, just below the diaphragm.
• The renal arteries carry oxygenated blood to the kidneys.
• The renal veins transport purified, deoxygenated blood away.
• A tube, the ureter, extends from each kidney to the bladder.
• The bladder is a thin walled muscular sac storing urine temporarily.
• The urethra transports urine from the bladder to the exterior.
• At the bladder base, a sphincter muscle regulates urine flow to the urethra.

Excretion in Humans

• Metabolic waste diffuses from cells to blood in blood vessels, via tissue fluid.
• Blood transports waste to excretory organs, which remove and release them.

Excretory Organs

• The lungs excrete CO2, water vapor, and heat.
• The kidneys excrete urine consisting of excess water, mineral salts, and nitrogenous wastes; stored in the bladder.
• The liver excretes urea and bile pigments. Urea is transported to the kidneys for excretion in urine. Bile pigments are excreted via feces.
• The skin excretes sweat with excess water, salts, and a bit of urea via the sweat glands.
• CO2 is a product of cellular respiration.
• Excess water comes from cellular respiration, food, and fluids.
• Urea forms in the liver from excess amino acids.
• Uric acid is the end product of nucleic acid metabolism.
• Creatinine comes from creatinine phosphate in cells.
• Bile pigments form in the liver from hemoglobin breakdown.

Metabolism

• Metabolism is all the chemical reactions continuously happening in cells.
• Metabolism produces CO2, excess water, salts, and nitrogenous wastes (i.e., urea, uric acid and creatinine).
• These metabolic wastes must be continuously removed, preventing poisoning and impaired function.
• Excretion is the removal of metabolic wastes from the body
• Egestion is the removal of undigested waste.
• Secretion is the release of useful substances secreted by cells.