3/16/2020

1

Excretory SystemExcretory SystemExcretion – removes cellular waste

The process that collects & removes harmful or useless substances that

form in the body or are taken into the body from the blood, tissues, and cells.

Humans must get rid of two types of wastes. Wastesfrom the digestive system (feces) and wastes frommetabolic activities (sweat & urine). Removingdigestive wastes (pooping) is called egestion, whileremoving metabolic wastes is called excretion.

Major metabolic wastes produced byhumans:

Water, Carbon dioxide, Salts, and UreaDehydration synthesis and respirationWaterCellular respiration Carbon dioxideNeutralization reactions Salts

Nitrogenous wastes1- Amino acidsDigestion of proteins amino acids.Human excrete minor amounts of some amino acids in the urine2- AmmoniaAmmonia is a poisonousDeamination of amino acids ammonia

3- UreaUrea is less toxic and more soluble in water than ammonia.Amino acid and purine bases metabolism UreaIn livers of mammals, urea is synthesized from ammonia through a series ofreactions known as urea cycle4- Uric acidIt excreted in crystalline form mixed with, but not dissolved in, small amountsof water.Metabolism of purine bases adenine and guanine Uric acid

Excretory SystemExcretory SystemAlthough the urinary system has a major role in excretion, other organs contribute to the excretory function.

3/16/2020

2

THE SKINThe skin excretes the sweat outside the body throughnumerous pores in the surface of this organ. Sweat is amixture of three metabolic wastes: water, salts, and urea. Soas you sweat, your body accomplishes two things: 1)sweating has a cooling effect on the body, and 2) metabolicwastes are excreted.

THE LUNGSCellular respiration occurs in every living cell in your body. Itis the reaction that provides energy) for cellular activities. Asrespiration occurs carbon dioxide is produced as a wasteproduct. As the carbon dioxide accumulates in body cells, iteventually diffuses out of the cells and into the bloodstream,which eventually circulates to the lungs. In the alveoli of thelungs, carbon dioxide diffuses from the blood, into the lungtissue, and then leaves the body every time weexhale. Some water vapor also exits the body duringexhalation

THE LIVERThe liver is a large, important organ in our bodies. Itsnumerous functions make it "part" of the circulatory,digestive, and excretory systems. Liver as an excretoryorgan acts to breakdown some proteins and othernitrogenous compounds by a process called deamination . As a result of these reactions, a nitrogenous waste called urea is formed . Liver as well as helps in excreting toxicsubstances, drugs, and their derivatives; and bile pigmentsand cholesterol

HUMAN EXCRETORY ORGANS Four Organs of the Excretory SystemFour Organs of the Excretory System

•The lungs in the respiratory system excrete some waste products, such as carbon dioxide and water. •The skin is another excretory organ that rids the body of wastes through the sweat glands. •The liver (via the intestines) excretes bile pigments that result from the destruction of hemoglobin. It also converts nitrogenous waste from the break down of proteins into urea.•The major task of excretion still belongs to the kidneys, the major organ in the urinary system. If it fails the other organs cannot take over and compensate adequately.

Cellular WasteCellular Waste

HeatWaterSaltsCO2

Urea

W/O excretion poisonous wastes build up in blood, cells, and tissues.Could lead to serious illness &

eventually DEATH!

Liver Liver –– Some FunctionsSome FunctionsFunctions in ExcretionFunctions in Excretion

–– Detoxifies BloodDetoxifies Blood

Filters Bacteria, alcohol, drugs, toxic Filters Bacteria, alcohol, drugs, toxic substancessubstances

Changes them into inactive or less toxic Changes them into inactive or less toxic forms.forms.

Excretes Bile

Contains

Worn-out RBC

Bile salts

Cholesterol

3/16/2020

3

Liver Produces UreaLiver Produces UreaFunctions in ExcretionFunctions in Excretion

–– Forms Forms UreaUrea

Changes toxic wastes (ammonia Changes toxic wastes (ammonia –– from break from break down of amino acids) to Urea.down of amino acids) to Urea.

Urea Urea Blood Blood KidneysKidneys

Filtered out & excreted in UrinFiltered out & excreted in Urinee

Lungs Lungs ––Main Function Main Function

Alveoli - Exchange O2 & CO2 between air and

blood (through process of diffusion)

Lungs excrete CO2 when you EXHALE

SkinSkinSweat GlandsSweat Glands

–– Help cool body: Heat escapes through Help cool body: Heat escapes through millions of pores in skin surfacemillions of pores in skin surface

–– Excrete perspiration (evap. cooling)Excrete perspiration (evap. cooling)

9999% H% H22OO

Mineral SaltsMineral Salts

UreaUrea

THE URINARY SYSTEM IN HUMAN

Structure

Two Kidneys

They are dark, red, bean-shaped and lie in the upper part ofthe abdominal cavity against the dorsal body wall (Fig. 9).They are embedded in a protective layer of fat and connectivetissue. The right kidney is slightly on a lower level than theleft. Each Kidney is about 4½ inches long, 2½ inches broad,and over one inch thick. The weight of each kidney in adulthuman is about 150 g, so they represent about 0.5% of thetotal weight of the body.Two UretersThey are two slender muscular tubes which take their origin atthe hilum of each kidney (from the renal pelvis) and run downto join the urinary bladder.The Urinary BladderThe bladder has an elastic wall and placed in the lower part ofthe abdominal cavity. It supplied with a sphincter muscles at itsconnection with both the ureters and urethra.The UrethraIt is a muscular tube which carried the urine from the bladderto the outsideRenal Vein and ArteryEach kidney receive a renal artery from the aorta, which bringsthe blood into the kidney. From each kidney, a renal vein isextended to the inferior vena cava, which carries the bloodback to the heart.

3/16/2020

4

Kidneys & Urinary SystemKidneys & Urinary System

Urinary System Urinary System –– excretes waste and excretes waste and maintains homeostasis maintains homeostasis of body fluidsof body fluids..

–– KidneysKidneys (main organ of the system)(main organ of the system)

–– UretersUreters

–– BladderBladder

–– UrethraUrethra

Kidneys & Urinary SystemKidneys & Urinary System

KidneysKidneys

–– Two Two

–– Fist sizedFist sized

–– Bean shapedBean shaped

KidneysKidneys-- Functional Units & ProductFunctional Units & Product

Nephron Nephron (about one million per kidney)(about one million per kidney)

–– Microscopic units that Microscopic units that filterfilter blood of wastes.blood of wastes.

–– HH22O and waste taken from blood into nephronO and waste taken from blood into nephronForm URINEForm URINE

Glomerulus (clump of capillaries)

At end of each nephron

Network of coiled tubes – diffusion of wastes -while useful substances & water are reabsorbed

Urine

Pale yellow solution

Urea, H20, salts, other trace solutions (toxins…)

Urinary System Urinary System -- continuedcontinued

UretersUreters–– Narrow muscular tubesNarrow muscular tubes

–– Connect Kidney Connect Kidney BladderBladder

Bladder

Muscular sac

Stores Urine

Expand to fill

Muscle relaxes

Urine squeezed into Urethra

3/16/2020

5

Urinary System Urinary System -- endpointendpoint

UrethraUrethra

–– Tube leading from Bladder Tube leading from Bladder outside of bodyoutside of body

THE KIDNEYINTERNAL STRUCTURE

An Outer CortexIt made of a dark red tissue, due to the presence ofall glomeruli which contain tufts of blood capillaries.The cortex contains all the proximal tubules anddistal tubules, and cortical collecting ducts.

An Inner MedullaIt is made of lighter tissue, due to its relative lowblood supply. Medulla has a radial appearance dueto the presence of loops of Henle, the vasa recta,and medullary collecting tubules. It is subdividedinto: (i) an outer medulla, which lies next to thecortex and (ii) an inner medulla which extends outinto the renal sinus forming renal papillae. Medulla isdifferentiated to form a number of cone-like structureknown as renal pyramids (10-15) with their apicalends projecting as renal papillae into the calyces ofthe pelvis.

The PelvisIt is a funnel-shaped structure which has at its freeend number of cup-like cavities called calyces (sing.calyx). The pelvis leads to the ureter.

PHYSIOLOGICAL FUNCTIONS OF KIDNEYS

Excretion of waste productsKidneys excrete the waste products such as nitrogen, sulphur, and ketone bodies. They aid in excretion of the drugs, toxicsubstances, and their derivatives, e.g. penicillin.

Maintenance of constant volume and composition of inside the bodyThe kidneys maintain constant volume of body fluids, osmotic pressure, and blood pressure, hence they protect the body fromdiseases, by excreting excess water and electrolytes.

Regulation of arterial blood pressureThe kidney regulates the lowered blood pressure via secretion of the enzyme renin, which activates the angiotensigogensystem

Regulation of blood pH through preserving acid-base balanceIn case of acidosis, the two kidney secrete H+ and react it with ammonia (NH3) forming ammonium (NH4), which excreted asNH4 salts in the urine. While, in case of alkalosis, the kidneys decrease the secretion of H+, synthesis of NH4, andreabsorption of bicarbonate (HCO3-).

Enzyme formationThe kidneys synthesize enzymes such as histaminase to destroy the histamine, phosphatase to remove inorganic phosphatefrom organic compounds, and cholinesterase to destroy acetylcholine.

Endocrine functionThey regulate the conversion of vitamin D to 1,25 dihyroxycholecalciferol (and also 24,25 dihyroxcholecalciferol) whichfacilitate the intestinal absorption of calcium and phosphate. It also acts on bone by mobilizing the calcium ion.

DetoxificationIn the kidney, the toxic substance is converted to a non-toxic compound. For example, the kidneys convert benzoic acid to thehippuric acid by combination with glycine and excrete it through urine to outside. This process occurs mainly in the liver.

Factors that affect kidney Factors that affect kidney functionfunction

Antidiuretic hormone (ADH) Antidiuretic hormone (ADH) –– prevents prevents excess water loss from kidneysexcess water loss from kidneys

Alcohol Alcohol –– inhibits secretion of ADH = more inhibits secretion of ADH = more urine volumeurine volume

Aldosterone Aldosterone –– prevents excess loss of prevents excess loss of sodium and water from kidneyssodium and water from kidneys

Caffeine Caffeine –– increases rate of salt and water increases rate of salt and water loss from kidneysloss from kidneys

Increased blood pressure Increased blood pressure –– increase rate of increase rate of water loss from kidneys.water loss from kidneys.

3/16/2020

6

THE NEPHRON

The substance of the kidney is made up of a number of structural and functional units called nephrons (Fig. 5). Each humankidney contains one million nephrons or more. The nephrons are concerned with the separation of urine from the blood.There are 2 basic types of nephrons:

Cortical nephrons: They represent 85% of the nephrons in the kidney. Except for a small portion of the loop of Henle,they're entirely located within the renal cortex. They will play a large role in making sure the blood has the correct ionic andchemical make-up.

Juxtamedullary nephrons: Their renal corpuscles are located very close to the cortex-medulla junction. Their loops ofHenle extend deep into the medulla and can be quite long. They play an important role in the body's ability to concentrateurine, i.e. they are very involved in water reabsorption.

Structure of the NephronI- Malpighian corpuscle

1- Bowman’s capsule2- Glomerulus

II- Coiled uriniferous tubules1- Proximal tubule2- Loops of Henle3- Distal tubule

III- Collecting tubule

URINE FORMATIONNephrons produce the urine through three main processes:(I) Filtration of water and dissolved substances from the

blood into Bowman’s capsule and this occursthrough the glomerulus.

(II) Reabsorption of water and solutes through theuriniferous tubules.

(III) Secretion into the lumen of the tubule of somesubstances formed by the tubule cells or which arecirculating in peritubular venous capillariessurrounding the distal tubule.

(I) Glomerular filtration of water and solutesfrom the blood● Rate of blood flow through the kidney = 1,300 ml per minute● Filtration rate = 125 ml of fluid per minute● The primary urine in Bowman’s capsule is identical in composition withthe plasma, but it is devoid of proteins (and other colloids).Mechanism of glomerular filtration: It depends on:(1) Mean blood pressure in the glomeruli.Blood pressure (hydrostatic pressure) in glomeruli capillaries is measuredto be 55 mmHg in normal condition.(2) Colloidal osmotic pressure.Colloidal osmotic pressure of the plasma proteins is equivalent of ahydrostatic pressure varying from 25-30 mm Hg. It opposes the filtrationpressure.(3) Pressure in the Bowman’s capsule.Hydrostatic pressure of the fluid in Bowman’s capsule is about 15 mm Hg.(4) Integrity (permeability) of the basement membrane.Normally, substances of smaller molecular weight like hemoglobin (68,000)can pass through the basement membrane.Glomerular filtration rate (GFR) = UxV / PxRenal clearance (RC) = UxV / Px

Effective filtration pressureBlood pressure or filtration pressure in glomeruli capillaries = 55 mmHg. The forces opposing this pressure are: (i) Colloid osmotic pressure of plasma proteins (30 mm Hg).(ii) Hydrostatic pressure of the fluid in the Bowman’s capsule (5 mm Hg).So, Effective filtration pressure = Glomerluar pressure – (Colloidal pressure + Capsular pressure) = 55 – (30 +15) = 10 mm Hg.

SEVENTH LECTURE

(II) Reabsorption of water and solutesthrough the uriniferous tubules

Role of proximal tubule

● Of the ~125 ml of plasma filtered by the glomeruli, 124 ml isreabsorbed during passage through the renal tubules.

● The process of tubular reabsorption of different substances(water, ions, and nutrients) may result from either active cellulartransport (via cotransporters) or passive back diffusion (via simplediffusion, facilitated diffusion, and osmosis.

● Along the tubule, glucose and amino acids (100%), sodium(65%), chloride (50%), water (65%), bicarbonate (90%),phosphate (partly), potassium (55%), urate (100%), urea (partly).