Module 15: Renal System

Kidney Function

Filter 200 liters of blood daily, maintain the proper balance between water & salts, & acids & bases. pH balance

Gluconeogenesis

Making new glucose

Cortex

Outer layer of the kidney

Medulla

Inner area of the kidney

Nephron

Functional filtration unit in the kidneys

Cortical nephrons

Main job is filtration. 80% of the nephrons in a kidney are almost completely contained within the cortex

Juxtamedullary nephrons

Establish an osmolarity gradient within the medulla 300-1200mOsM allows us to concentrate the filtrate. 20% dip down into medulla

Filtrate

Material that we filtered

Bowman’s capsule

The nephrons begins with a hollow, ball-like structure that surrounds the glomerulus. The only area where filtration is going to occur

Proximal convoluted tubule (PCT)

consists of cuboidal cells with numerous microvilli and mitochondria. High surface area. Most material reabsorbed here automatically (obligatory Reabsorption)

Loop of Henle

Hair-pin shaped segment that dips down towed the medulla and then back up

Descending loop of Henle (DLOH)

Thin segment correlates with simple squamous cells that allow for water reabsorption. Permeable to water but not solutes

Ascending Loop of Henle (ALOH)

Thick segment. Consists of cuboidal and columnar cells. Reabsorption of electrolytes like sodium, potassium, and calcium. Permeable to solutes but not water.

Obligatory Reabsorption

Reabsorption that is independent of the needs of body, reabsorbed whether you need it or not (still require proteins). Happens at proximal convoluted tubule (PCT) through ascending loop of henle

Selective Reabsorption

After the ascending loop of Henle (DCT,CD) . Dependent on the needs of the body and under hormonal control

Symport SGLT protein

Sodium-glucose-linked transporter (Apical side). Use the potential energy of the Na+ gradient. Na+ comes in down its gradient and you’re pulling glucose up a gradient for the ride.

GLUT protein

Glucose uniport transporter (Basolateral side). Allows glucose to go down a gradient into the ISF

Distal convoluted tubule (DCT)

Consists of cuboidal cells without microvilli. Measures if you need more electrolytes (Na+). Site of more secretion vs absorption. Absorption under hormonal control (selective Reabsorption)

Afferent Arteriole

Larger arteriole that brings brings blood to glomerulus

Glomerulus

Knot of capillaries (fenestrated). Start and end with Arteriole. High BP. Fluids and solutes are forced out of the blood throughout the entire length of this

Efferent Arteriole

Blood leaving the glomerulus. Lower blood pressure → slower flow

Peritubular capillaries

Low-pressure, porous capillaries adopted for absorption, arise from efferent arterioles, cling to adjacent renal tubules, empty into the renal venous system

Vasa-Recta

Long, straight efferent arterioles of juxtamedullary nephrons

Collecting duct

Receive filtration from multiple nephrons

Filtration

Fluid and small solutes from the blood plasma are pushed into the tubules of the nephrons. Vascular → tubular

Reabsorption

Reclamation of needed recourses that were initially filtered out. Can be passive active transport. Facilitated by the low BP and flow in the peritubular capillaries and vasa recta. Obligatory/selective

Secretion

Cell gets rid of material. Active process that involves the movement of molecules from the extracellular fluid into the lumen of the nephron. Important in homeostatic regulation of K+ and H+

Inulin

Non-invasive way to test GFR. Plant based polysaccharide that is filtered but not reabsorbed or secreted to determine baseline. Clearance will be 125mL/min

Excretion

Expulsion of material from the body (not from an individual cell). =Filtration - Reabsorption + secretion

Fenestratons

Allow a higher throughput for filtration

Basal lamina

Extracellular mesh work of proteins. Negative charge → repels the neg. Charge found on plasma proteins

Podocytes

Partially block the fenestrations

Filtration slit

Very narrow avenue where material can go into the bowman’s capsule

Filtrate

The plasma and solutes in plasma that gets moved into the bowman’s capsule

Net Filtration Pressure (NFR)

= HP(out) - COP(in) - PBC(in). Dictate how well the nephron (kidneys) handle filtration

Glomerular Filtration Rate (GFR)

Most heavily influenced by NFR. The total amount of filtrate formed per minute by the kidneys (normally 120-125mL/min)

Granular Cells

In endothelium of afferent arteriole. Secrete Renin and paracrine signals. Have mechanoreceptors (stretch receptors)

Macula densa cells

In the ALOH, chemoreceptors that detect Cl-. Detect how fast Cl- zips by in the filtrate and release paracrine signals to afferent arteriole

Myogenic contraction

When HP is elevated in afferent arteriole the smooth muscle is stretched→ smooth muscle responds by contraction

Renal Autoregulation

A local control process in which the kidney maintains a relatively contrast GFR in the face of normal fluctuations in blood pressure

Flow-dependent Tubuloglomerular Feedback

A paracrine control of the granular cells and smooth muscle in the afferent and efferent arterioles, sensing the flow rate of Cl- in the filtrate by the macula densa cells

Renin

Hormone releases by granular cells, released when blood pressure is low. Helps activate a inactive plasma protein (liver) Angiotensinogen

Angiotensinogen

Inactive plasma protein secreted from the liver

Angiotensin I (ANG I)

Weak signal molecule activated from Angiotensinogen plasma protein. Requires a sequential activation/further activated by 2nd enzyme

Angiotensin-converting Enzyme (ACE)

Enzyme that converts Angiotensin I (ANG I) to Angiotensin II (ANG II).

Angiotensin II (ANG II)

Very active form of Angiotensinogen. 1.targets cardiovascular control center in brain (CVCC) 2.signal systemic arterioles 3.signal hypothalamus 4.signal adrenal cortex

Vasopressin (ADH)

Made in the Hypothalamus and transported and released by the post-pituitary. Target the collecting duct to promote water reabsorption. Allows for insertion of water channels called aquaporins, in the apical surface of the epithelial cells, increasing water permeability

Diuresis

Increased production of urine

Reabsorption Transcellular Method

Substances cross the apical and basolateral membranes of the tubule cells through channels or carrier proteins

Reabsorption Paracellular Method

Certain substances can pass between cells through junctions

Saturation

Refers to maximum rate of transport when all available carriers occupied (transport maximum)

Renal threshold

Plasma concentration of substance, that once filtered would lead to saturation in the nephron

Specificity

Each carrier binds to a transports small subset of solutes

Competition

Similar shaped molecules or antagonists may block transport

Aldosterone

Hormone (made in adrenal cortex) targets the cells in the DCT and beginning part of the collecting duct. Promotes selective reabsorption of Na+. And secretion of K+

Parathyroid hormone

Hormone targets cells in the DCT to promote Ca2+ reabsorption

Atrial natriuretic peptide (ANP)

Opposes that of Aldosterone. Hormone kicks in when you have too much Na+. Promotes Na+ secretion and excretion. Reduce blood Na+ which decreases blood volume and lowers blood pressure

Buffers

Work super fast but get overwhelmed easily like within the 1st second bc you have a finite amount of buffers. HCO3- (plasma and ISF), cellular proteins (ICF), and phosphate ions/ammonia (filtrate) moderate changes in pH

Ventilation

Rapid response that occurs once buffering capacity is overwhelmed. Responsible for mitigating 75% of disturbances, primarily pH disturbances arising from metabolic issues. Manipulation in CO2

Renal system

Slowest, allowing for the direct secretion or a reabsorption of H+ and indirectly controlling HCO3- reabsorption/secretion. Compensates for pH disturbances due to respiratory issues or long-term

Urochrome

Yellow pigment responsible for the normal yellow color of urine. Concentration can be affected by drugs, vitamins supplements, diet, and birth control. Should be slightly acidic

Dilute urine

Filtrate is diluted in the ALOH, ADH is not being secreted, collecting ducts remain impermeable to water(no water reabsorption), and osmolarity can be as low as 50mOsM

Concentrated urine

ADH inhibits diuresis, increased # of aquaporins present on plasma membrane, up to 99% of water in the filtrate is reabsorbed, and depends on the high medullary osmotic gradient