DAT Biology: Excretory System

Excretion

Process by which metabolic wastes are filtered out of the blood and removed from the body as urine

Kidney

Responsible for the filtration of the blood and the preparation of a urine product for excretion

Regulates blood pressure, pH, and stimulates generation of red blood cells

Structural Components: Outer Cortex and Inner Medulla

Nephron

Functional unit of the kidney

Main Structures: glomerulus, proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting duct

Renal Corpuscle

First structure of the nephron containing the glomerulus and Bowman’s capsule

Site of filtration within the renal CORTEX

Glomerulus

Series of capillaries existing within the renal corpus, surrounded by Bowman’s capsule

Bowman’s Cpasule

Surroundings the glomerulus, part of the renal corpuscle, where you see some filtration of the blood

Afferent Arteriole

Blood vasculature that enters the renal corpuscle providing nutrient-rich blood for filtration

Podocytes

Foot-like processes that form a fenestrated filtratino barrier, providing specificity to filtration. increasing filtration selectivity in the renal corpuscle

Efferent Arteriole

Blood vasculature that exits the renal corpuscle, can form the peritubular capillaries or the vasa recta

Peritubular Capillaries

Blood vessels surrounding the convoluted tubules

Convoluted Tubules

Winding, coiled sections of the kidney’s plumbing system that processes fluid after blood is filtered in the Bowman’s capsule

Vasa Recta

Blood vessels surrounding the loop of Henle

Proximal Convoluted Tubule

Site of the majority of reabsorption via active transport and cotransport

• Reabsorbed: Na+, Cl-, 100% of reabsorbed glucose and amino acids

• Secreted: H+

Loop of Henle

After proximal convoluted tubule, it is the nephron tube that descends into the kidney medulla and exists between the convoluted tubules

Contains a descending and ascending limb

Descending Limb

Descends into the medulla from the proximal convoluted tubule, first part of loop of Henle

Permeable to water, water flows out of the urine into the blood and urine concentration increases

Ascending Limb

Ascends out of the medulla connecting to the distal convoluted tubule, second part of the loop of Henle

Impermeable to water, ions and salts flow out of the urine so urine concentration decreases

Distal Convoluted Tubule

Reabsorption of Na+ and Cl-, secretion of K+ and H+, water passively follows reabsorbed salts

Collecting Duct

Bulk passive reabsorption of water, secretion of K+

Urine concentration increases

Excretory Hormones

Capable of maintaining blood volume and blood pressure as well as the relative concentrations of molecules and substrates within the blood and the filtrate

Renin-Angiotensin-Aldosteron System

System of hormones, tissues, and organs capable of increasing blood pressure in response to detected low blood pressure

Juxtaglomerular Cells

Modified smooth muscle cells associated with the afferent arteriole

Capable of detecting changes in bp and blood volume

Release renin in times of low blood pressure

Renin

Enzyme capable of converting angiotensinogen (released from the liver) into its activated form, angiotensin I, also often stimulated by fight/flight response

Angiotensin Converting Enzyme (ACE)

Enzyme capable of converting angiotensin I into angiotensin II, released from walls of blood vessels in the lungs

Angiotensin II

Increases blood pressure and blood volume

Aldosterone

Mineralcorticoid released from the adrenal gland that affects the kidney, acting on distal tubules and collecting ducts of nephrons

Actions at Nephron: increase water and soidum reabsorption and increases potassium secretion

Antidiuretic Hormone (ADH or V asopressin)

Produced in hypothalamus

Stored and released by the posterior pituitary gland

Capable of increasing blood volume and pressure

Effect: increases aquaporin channel presence within the collecting ducts, increasing water absorption

Alcohol

Inhibitor of ADH, less water is reabsorbed, causing increased urination

Atrial Natriuretic Peptide (ANP)

Produced by the cells of the heart atrial cells in response atrial distension caused by increased blood volume and pressure

Atrial Distension

Stretching or enlarging of an upper heart chamber (atrium), when too much blood/pressure pushes against inner walls of heart.

Over time, stretching can change the heart’s shape and lead to rhythm problems.

Osmoregulation

Maintenance of internal water balance by an organism, achieved by absorption and secretion of water and solutes

Impacted by water/solute concentrations of the surrounding environment

Hypotonic Solution

Lower solute concentration than inside of the cell, causing water to rush into the cell, making the cell swell and potentially burst (lysis)

Isotonic Solution

Same solute concentration as cell, resulting in no net movement of water across the cell membrane, and cell maintains normal shape and volume

Hypertonic Solution

Has higher solute concentration than inside of the cell, pulling water out of the cell via osmosis, causing the cell to shrink and shrivel.