Kidney Function and Homeostasis

Kidney

• Excretion eliminates unwanted substances and metabolic wastes.
• During metabolic processes, tissues generate waste, including carbon dioxide, undigested food, heavy metals, drugs, toxins, and pathogenic organisms.
• Key excretory organs in the body are digestive system, lungs, skin, and liver.
• The renal system has the highest excretory capacity and is vital for homeostasis.
• The renal system comprises a pair of kidneys, ureters, a urinary bladder, and a urethra.
• Kidneys form urine, ureters transport it to the bladder, the bladder stores urine, and the urethra voids it.

Functions of Kidney

• Kidneys maintain homeostasis by regulating body activities during urine formation.

Role in Homeostasis

• Kidneys excrete waste products by forming urine - these products derive from metabolic activities.
• They also excrete toxins, drugs, heavy metals, and pesticides.
• Kidneys maintain water balance by conserving water when it's scarce and excreting it when it's in excess.
• These kidneys also retain sodium when body water osmolarity decreases and eliminate it with increased osmolarity for electrolyte balance.
• The kidneys, lungs, and blood buffers prevent acidosis, and kidneys can eliminate sulfuric and phosphoric acids.

Hemopoietic Function

• Erythropoietin helps stimulates the production of erythrocytes.
• Thrombopoietin helps stimulate the production of thrombocytes.

Endocrine Function

• The kidneys also secrete hormonal substances such as erythropoietin, thrombopoietin, renin, 1,25-dihydroxycholecalciferol (calcitriol), and Prostaglandins.

Regulation of Blood Pressure

• Kidneys regulate arterial blood pressure in the long term by regulating extracellular fluid volume.
• Kidneys also regulate indirectly through renin-angiotensin mechanism
• Regulation of Blood Calcium Level
• Vitamin D is necessary for intestine to absorbs calcium and kidneys regulate blood calcium through activation of 1,25-dihydroxycholecalciferol into vitamin D.

Functional Anatomy of Kidney

• The kidney is a compound tubular gland covered by connective tissue.
• The hilum is on the medial border where the renal artery, renal veins, nerves and ureter pass.

Different Layers of Kidney

• The outer cortex has a dark, granular appearance - it contains renal corpuscles and convoluted tubules.
• The renal columns, or columns of Bertini, are cortical tissue penetrate the medulla.
• The inner medulla has tubular and vascular structures in parallel radial lines, forming 8-18 medullary or Malpighian pyramids.
• The broad pyramid base touches the cortex, and the apex projects to the minor calyx.

Renal Sinus

• Has the following structures: renal pelvis (upper, expanded ureter part); subdivisions of pelvis: 2-3 major and ~8 minor calyces - nerve/artery branches and vein tributaries, connective tissues and fat.

Tubular Structures of Kidney

• Composed of closely arranged uriniferous tubules, with blood vessels and interstitial connective tissues in between.
• The structures include nephrons (terminal or secretary tubules for urine formation) and collecting ducts/tubules (for urine transport to the ureter pelvis).
• Collecting ducts lead to the ducts of Bellini, opening into minor calyces through the papilla.

Nephron

• The nephron is the kidney's structural and functional unit and is formed by two parts.
• There are 1 to 1.3 million nephrons in each kindey.
• A blind end called renal corpuscle or Malpighian corpuscle- and a tubular portion called renal tubule.

Renal Corpuscle

• The renal or Malpighian corpuscle is spheroidal, slightly flattened, ~200 μ in diameter, and filters blood, initiating urine formation.

Situation of Renal Corpuscle and Types of Nephron

• The renal corpuscle is always in the cortex, either near the periphery or medulla.

Classification of Nephrons

• Cortical nephrons have corpuscles in the outer cortex near the periphery (85% in human kidneys).
• Juxtamedullary nephrons corpuscles are the inner cortex near the junction between the cortex and medulla.

Structure of Renal Corpuscle

• Formed by two portions: Glomerulus and Bowman capsule.

Glomerulus

• Glomerulus is a tuft of capillaries enclosed by Bowmans capsule.
• The vascular system in the glomerulus is purely arterial.
• Glomerular capillaries come from the afferent arteriole, and leave the Bowman capsule by the efferent arteriole.

Tubular Portion of Nephron

• Continues from the Bowman capsule and has three sections: proximal convoluted tubule, Loop of Henle, and distal convoluted tubule.

Proximal Convoluted Tubule

• Arises from the Bowman capsule, located in the cortex, continuing descends as the limb of Henle loop.
• It is ~14 mm long with a ~55 μ diameter; it is formed by a cuboidal epithelial cell layer with hair-like projections directed tubular lumen

Loop of Henle

• Consists of a descending and ascending limb connected by a hairpin bend.

Descending and Ascending Limb

• Made up of a Thick and thin segment. Total length is 10mm to 15mm.
• The macula densa is in the terminal portion of ascending segment runs between arterioles.

Length and Extent of Loop of Henle

• Short hairpin bend, penetrates only up to the outer medulla in cortical nephrons.

Distal Convoluted Tubule

• Continuous with thick ascending segment, in the cortex, continues a collecting duct.
• It is 14.5-15 mm long and a 22-50 μ diameter; has a cuboidal epithelial cell layer without a brush border, called intercalated cells or I cells.

Collecting Duct

• The initial/arched collecting duct is continuous to collecting. The lower part of the collecting duct is in the medulla. Collecting ducts unite to the straight one in the medulla.
• Collecting duct features: Length is 20-22 mm, with a 40-200 μ diameter and Cuboidal/columnar epithelial cells.

Passage of Urine

• Straight collecting ducts join to form papillary ducts/ducts of Bellini where in the medulla inner zone, which open into a 'V' shaped papilla area collecting urine.
• Three or four combine minor calyces unite form one major calyx. Each Kidney has approximately 8 minor calyces and 2 to 3 major ones.
• From minor calyces, urine goes to into major ones and opens into the ureter pelvis (expanded ureter in the renal sinus, and then to the urinary bladder.

Juxtaglomerular Apparatus

• It is a specialized "near" organ, the glomerulus of each nephron.

Structure

• Three structures formed by the juxtaglomerular apparatus (macula densa, extraglomerular mesangial cells, and juxtaglomerular cells) that forms the apparatus.

Macula Densa

• The end of thick ascending segment is prior to it opening to the convoluted tubule. Located between afferent and efferent arterioles of same nephron which packed cuboidal cells.

Extraglomerular Mesangial Cells

• In the triangular location by the afferent, efferent arteriole, macula densa, they are called agranular, lacis, or Goormaghtigh cells.
• Glomerular mesangial cells are within glomerular capillaries. In a mesh they connect to the capillaries, and these regulate via their contractility.

Juxtaglomerular Cells

• These are specialized smooth muscle cells in the afferent wall before Bowman capsule. They are granular with tunica a media, in the walls of the afferent arteriole.

Polar Cushion Or Polkissen

• Forms a cap that is thick that surrounds the arteriole; it is in Bowman capsule.

Functions

• It is mainly that hormones are secreted, the the glomerular flow and filtration rates are regulated.
• Secretes Renin and Prostaglandins.

Renal Circulation

• Highly specialized blood facilitates the functions of the kidney that helps formulate urine.

Renal Blood Vessels

• Direct renal arteries go from hilus to kidneys that supply them.

Renal Artery

• Starts from an abdominal aorta and then passes the renal hilus and forms arteries that are segmental.

Segmental Artery

• Starts interlobar arteries (Fig 51.1).

Interlobar Artery

• Passes in between the medullary pyramids, turns at the pyramid, and creates arcuate artery.

Arcuate Artery

• Creates arteries interlobular.

Interlobular Artery

• Runs cortex that is renal and many arterioles start from each artery.

Afferent Arteriole

• Enters capsule Bowman creating glomerular, and then splits four, large capillaries

Glomerular Capillaries

• These small glomerular create capillary loops, and then lead to efferent arteriole and leave by Bowman capsule. Next are the Efferent Arteriole, forms capillary.

Peritubular Capillaries and Vasa Recta

• Peritubular form the cortical nephrons where as juctamedullary supplied by the vasa recta which straight as from efferent.

Venous System

• Peritubular and the vasa recta feed into the venous, starts through veins interlobular, it continues through the arcuate, interlobar, veins, segmental and vein (renal). The renal vein from comes from the kidney via the inferior vena cava.

Measurement of Renal Blood Flow

• With plasma clearance that is PAH it is measures, see the Chapter 55

Regulation of Renal Blood Flow

• Kidneys mainly autoregulate blood. The renal blood vessels are not highly innervated.

Autoregulation

• Organs such as the kidney is given intrinsic control by the own blood flow (Chapter 102). High efficiencies in the kidneys.

Renal Autoregulation

• Important for maintain the GFRs, kidneys can be stable during blood (60-180mmHg)

Mechanisms of GFR

• Myogenic Response Stretches elastic affarent, increases Ca inflow, which then leads to muscle constriction reduces BF into the glomeruarlues.
• Tubuloglomerular Feedback Macula in turn controls with GFR and GFR.

Special Features of Renal Circulation

Renal circulation has to cope with the functions of the kidneys. Therefore

• Renal areteires can be direcly come from the aorta. So high in aorta leads to greater blood through the kidneys.
• About 1,300 mL of output that is cardiac, The kidneys then are receive the most ammount of heart.
• A blood that flows into the kidney has pass through the capillaries, because then the blood is filtered to renal.
• Portal system through double network capilaries, Glomerular and the peritubular.
• High in capillary has a hgih pressure (60-70) which means afferent is a smalle diameter than other capillary in body.
• Pressure has low amount with is around 8-10mm Hg, so a tubal allows reabsorpton.
• Autoregulation helps to estabish flow.

Urine Formation

• Urine formation is a cleaning activity of the blood. 1,300 ml of enters in the blood goes into kidneys, wastes and other waste through normal urine of 1liter to 1.5 liter.

Formation Processes

• The capillary is filtered into bowman capsule and the process then in urine Then filtrate which tubular can absorb quality where the amino acids, water etc is called reabsorbtion.
• Which the secretion it takes waste goes there too named, this three helps.

Glomerular Filtration

• is which happens the blood the pores passes, its the formation the filtering membrane.

Filtration Membrane

• The three layers are The pores (fenstrae are about 0.1 μ)
• Membrane that is in the basement layers Layer visceral of Bownams, where each call is pedicles also filtration called filtration.

Processes of Filtration

• The substancess has the filtration as well there.

Ultrafiltration

• Glomeuraular, does remove proteins.
• The particles is protein prevent.
• Glomelrus proteins do remove.

Methods

• Animals gets this, by micro pipete.
• The gormulae 125 = liters per day.

Filtration

• Amount of flow in ratio.
• The gormulae

Pressure

• Capillary pressure.
• Osmotic in the glomurlais.
• Hydro pressure in the capsule bowman. These pressires that affect how good it is or bad.

Capillary pressure

• Caused by 60 mm Hg its good glomerlars.

Capillary Pressure

There willl 2hgs the osmosis and they do remain in the cappilarieas.

Bowman Capsule

• Capusaular about is to 15mm hg.

Reabsorption of Sodium

• For ths filter by to do sodium reabsorption occur.
• And by the pump Na (sodium). The interstituimin there is a a small.

Reabsorption of Water

At the proximaul and this is with ADH, water absorbtion.

Act of ADH

Throught aquaportion. ADH by to vasopression 2, increases cyclic AMP and then the abrorptions

Reabsorption of Glucose;

• Transported transport SDC (sodium), and they can use another tranposrter to (GLUT2) called

Tubular Maximum

• Transport amount substance So it that is max rate amount reasbsorb glucose. There of 735m and for is 300m. Hormonal Factors: Some is that control.

Substance is Value Based

High, Sub, Non. To there actions is related. GlomerulotubularBalance

Explore the kidney's vital role in maintaining homeostasis, acid-base balance, and hemopoiesis. Understand the impact of kidney disease and genetic disorders on kidney function. Learn about renal excretion and adaptation mechanisms for survival.