BM108 Block E

Purpose of the renal system

Forms urine to remove waste, regulates blood volume and pressure, regulates plasma ion conc., regulates blood pH

Aorta

Main artery that takes oxygenated blood from heart → body

ADH (affect on urine)

Increases water reabsorption in distal convoluted tubule. Causes urine to become more concentrated

Arteriole constriction

Determines blood pressure

Renal system components

Kidney, ureters, urinary bladder, urethra

Kidneys arterial blood supply

received from the renal system, 1200-2000 litres per day

Renal medulla, and renal cortex

Kidneys two distinct regions of urine production

Nephron

Functional unit of the kidney

Nephron (structure)

one cell thick, several million in each kidney

Four main parts of the nephron

Renal corpsucle (glomerulus, and bowmans capsule), proximal convoluted tubule, loop of henle, distal convoluted tubule

Renal corpsucle components

bowmans capsule, glomerelus

renal corpsucle (overview)

glomerelus is a cluster of capillary loops enclosed by bowmans capsule. blood enters by afferent arterioles, and leaves via efferent arterioles

Proximal convoluted tubule

First segment of renal tubule, the convoluted portion of the tubule leads into a segment that descends into the medulla and becomes the loop of Henle

Loop of Henle

Forms a hair-pin structure that dips into the medulla and then ascends toward the cortex parallel to the descending limb

Distal convoluted tubule

Shorter and less convoluted than the PCT. The initial segment lies next to the glomerelus and is known as the juxtaglomerular apparatus (JGA)

Processes in the nephron

Filtration, reabsorption, secretion, excretion

Filtration

Many small solutes and water are filtered from the body fluids and enter the lumen of an excretory tubule

Reabsorption

Useful solutes and much of the water are transported across the epithelial cell layer of the tubule and returned to the body fluids

Secretion

Additional unwanted solutes are actively removed from body fluids and enter the lumen of the excretory tubule

Excretion

A portion of the filtrate including waste gets excreted as urine

Renal cortex

Primary site of blood filtration

Renal medulla

Filtrate becomes concentrated by reabsorption

Glomerular filtration

Blood plasma is filtered into renal tubule from glomerulus to form filtrate. Filtrate has same composition as plasma, high blood pressure in glomerulus forces fluid into renal tubule

Glomerular Filtration Rate (GFR)

Rate of filtrate production, controlled by dilation or constriction of afferent arteriole

Histology of renal corpsucle

Reabsorption major recovery of solutes

Passive; water, K+, HCO3-. Active; Glucose, amino acids, proteins, vitamins, NaCl

Secretion major recover of solutes

Passive; ammonia (NH3). Active; H+

Excretion solutes

Toxic substances, drugs, excess K+ and H+ ions

Loop of Henle - Descending limb

Thin, so it’s permeable to urea and water but not solutes. Passive water reabsorption occurs by osmosis, requires interstitial fluid to be hypertonic to filtrate for movement of water to occur

Loop of henle - ascending limb

Permeable to solutes but not water. Passive NaCl reabsorption in thin segment, active NaCl reabsorption in thick segment.

Loop of henle - countercurrent exchange system

In ascending limb ions move out resulting in osmolarity of interstitial fluid increasing in a gradient. This allows osmosis in descending limb

Loop of Henle - Countercurrent multiplier

active process which increases solute and ion in the interstitium of the medulla. Allows the nephron to reabsorb more water and concentrate the urine using little energy

Distal convoluted tubule - ion concentration

Further selective secretion of H+ and K+. Regulation of K+ conc and pH of blood. Reabsorption of HCO3- dependent on pH. Further reabsorption of Na+ and H2O

Collecting duct

Permeable to water but not solutes, passive water reabsorption. Far end becomes permeable to urea so some can get reabsorbed. Helps maintain concentration gradient

Juxtagomerular Apparatus (JGA)

Distal tubule contacts afferent arteriole at renal corpsucle. Purpose is to maintain blood pressure ensure proper GFR and efficient sodium reabsorption

Juxtaglomerular apparatus (JGA) composition

Macula densa (MD) tubular cells, Juxtaglomerular (JG) or granular cells, mesenglial cells

Macula Densa (MD)

Special cells in the wall of the DCT. Monitor the osmotic potential n filtrate, stimulate JG cells

Juxtaglomerular cells (JG)

When stimulated release renin if filtrate is too dilute, indicating insufficient filtration and/or low blood pressure/volume.

Mesenglial cells

Found between affarent and efferent arterioles. Specialised smooth muscle cells that also help with blood flow

HPA axis (Hypothalamic-Pituitary-Adrenal axis)

Body’s main way of responding to stress by releasing hormones that raise cortisol. Releases ADH

Antidiuretic Hormone (ADH)

Released by HPA axis, regulates volume and osmolarity of urine. Released when blood osmolarity is high, activates DCT and collecting duct increasing water retention.

Renin-angiotensin-aldosterone system (RAAS)

Essential for regulating blood pressure/volume, consists of renin, angiotensin II, and aldosterone.

Renin

Enzyme produced by kidneys. Released when low arteriole BP, converts angiotensinogen→angiotensin II. Stimulates aldosterone

Angiotensin II

Hormone that causes arteriole constriction (so increased blood pressure/volume). Causes increased NaCl and water retention in PCT

Aldosterone

Stimulated by renin; hormone produced by adrenal glands. manages Na+ and K+ levels. Increases NaCl and water reabsorption in DCT

Cardiovascular system (overview)

Transports nutrients and materials via blood

Components of blood

Fluid connective tissue, (after centrifugation) 3 layers are visible; plasma, leucocytes, erythrocytes, platelets not visible

Blood plasma

30-60% of total blood volume, water dissolved organic and inorganic nutrients, dissolved O2 waste products of metabolism, hormones, proteins, pH buffers

Blood leucocytes

Defend body against infection and disease

Erythrocytes (RBCs)

deliver oxygen to cells, and carry away carbon dioxide. Contains a high concentration of haemeglobin

Haematocrit

Volume of blood composed of red blood cells/erythrocytes (40-65%)

Haemaglobin

Contains 4 protein subunits. each subunit contains one heme molecule that binds O2. Each haemoglobin molecule can bind 4 O2 molecules

Capillaries

Site of gas and nutrient exchange

Platelets

Play a crucial role in the formation of blood clots

Distribution of blood at rest

Some organs (kidney, liver, GI tract) receive blood in excess of their needs. Brain can least tolerate disrupted blood supply, if brain’s blood supply is disrupted >4 min irrepairable damage caused.

Distribution of blood at rest - Lungs

Left side = 100%

Distribution of blood at rest - Digestive system

Right side = 21%

Distribution of blood at rest - Liver

Filters digestive systems blood, right side = 6%

Distribution of blood at rest - Kidneys

right side = 20%

Distribution of blood at rest = skin

right side = 9%

Distribution of blood at rest = brain

right side = 13%

Distribution of blood at rest = heart muscle

right side 3%

Distribution of blood at rest = skeletal muscle

Right side = 15%

Distribution of blood at rest = bone

right side = 5%

Distribution of blood at rest = other

Right side = 8%

Blood pressure formula

Flow = pressure gradient/resistance

Pressure gradient

Difference in pressure between beginning and end of a vessel

Resistance

Measure of hindrance, or opposition to blood flow through a vessel. Caused by friction between blood and vessel wall. If resistance increases, flow decreases.

Main determinants of resistance

Viscosity of blood, length of blood vessel, radius of the blood vessel.

Relationship of flow to resistance

Resistance ∝ 1/r4 - Slight change in radius produces significant change in blood flow

Vascular tree - consists of…

Arteries, arterioles, capillaries, venules, veins

Vascular tree - arteries

carries blood away from heart to tissues

Vascular tree - arterioles

Smaller branch of arteries

Vascular tree - capillaries

smaller branch of arterioles, smallest vessels across which all exchanges are made with surrounding cells

Vascular tree - venules

formed when capillaries rejoin, return blood to heart

Vascular tree - veins

formed when venules merge, return blood to heart

Arteries

Serve as rapid-transit passageways for blood from heart to organs. Have a large radius and low resistance. Acts as a pressure resevoir to provide driving force for blood when heart is relaxing

Arterial connective tissue contains:

Collagen fibres (provide tensile strength), elastin fibres (provide elasticity to arterial walls)

Systolic pressure

Peak pressure when blood is ejected

Diastolic pressure

Minimum pressure when blood is draining off into vessels downstream

Normal blood pressure

120/70mmHg (systolic/diastolic)

High blood pressure

>140/90mmHg (~40% of UK population)

Factors affecting blood pressure

Peripheral vascular resistance, cardiac output, blood volume, vessel elasticity

Peripheral vascular resistance

diameter of blood vessels

Arterioles (overview)

Major resistance vessels, convert pulsatile systolic to diastolic pressure swings in the arteries into the non-fluctuating pressure present in the capillaries.

Arteriole radius

Can be adjusted to distribute cardiac output among systemic organs depending on body’s momentary needs. Helps regulate arterial blood pressure

Arteriolar vasoconstriction

Caused by increased myogenic activity, oxygen, endothelin, sympathetic stimulation, and decreased carbon dioxide (and other metabolites)

Arteriolar vasodilation

caused by decreased myogenic activity, O2, sympathetic stimulation, and increased CO2 (and other metabolites), and nitric oxide

Internal core temp

37*c

Outer shell temperature

Consists of skin and subcutaneous fat, temp varies between 20-40*c

Thermoregulation - increase in core temperature

Speeds up cellular chemical reactions, more serious than cooling. Leads to nerve malfunction, and irreversible protein denaturation

Internal body temperature 41*c

Causes convulsions

Internal body temperature 43*c

Upper limit compatible with life

Thermoregulation decrease in core temperature

Slows down cellular reactions, pronounced prolonged fall in body temperature slows metabolism to fatal level

Four mechanisms of heat transfer

Radiation, conduction, convection, evaporation

Hypothalamus

Acts as a thermostat that speeds up heat loss/production as needed

Two methods of hypothalamus activation

Thermal receptors in skin provide input to central command, and direct stimulation of hypothalamus through changes in blood temperature perfusing this area

Types of extracellular communication

Endocrine system (endocrine signalling), nervous system (neural signalling)

Neural signalling

Uses electrochemical process to communicate via nerve cells using action potential and synaptic transmission