Lecture outline
Topic Overview of the Excretory system And structure of kidney
Lecture Objectives:
At the end of lecture student will able:
•
To define the process of excretion.
•
To enumerates the structure involve in the process.
•
To describe the features of kidney .
•
To discuss the functional unit of kidney.
Over View of Excretory System &Structure of kidney
•
Introduction
•
The kidneys are perfect examples of homeostatic organs
•
Maintain constancy of fluids in our internal environment
•
Filter 200 liters of fluid a day
•
Remove toxins, metabolic wastes, and excess ions to leave the body in urine
•
Return needed substances to the blood
•
A primary organ of excretion
•
Kidney Functions
•
Kidneys regulate volume and chemical makeup of the blood
•
Maintain the proper balance between water and salts as well as between acids and bases
•
Gluconeogenesis - supply glucose during fasting
•
Produce enzyme renin which helps regulate blood pressure and kidney function
•
Produce hormone erythropoietin which stimulates red blood cell production
•
Urinary System Organs
•
Structures of the urinary system include;
–
Kidneys
–
Urinary bladder
–
Ureters
–
Urethra
•
Kidney Location
•
The kidneys extend approximately from the level of the 12th thoracic vertebra to the third
lumbar vertebra
•
They receive some protection from ribs
•
Kidney Location
•
The right lies somewhat lower than left as it is positioned under liver
•
The lateral surface of each kidney is convex, while the medial is concave
•
External Anatomy
•
The adult kidney weights about 150 g (5 oz.)
•
Dimensions are 12 cm long, 6 cm wide, 3 cm thick
•
External Anatomy
•
Medial surface has a vertical cleft called the renal hilus that leads into the space within
the kidney called the renal sinus
•
Atop each kidney is an adrenal gland which is unrelated to kidney function
•
External Anatomy
•
Structures such as the ureters, the renal blood vessels, lymphatics, and nerves enter the
kidney at the hilus
•
These structures occupy the renal sinus
•
Position of the Kidneys
•
The kidneys are retroperitoneal, or behind the peritoneum
•
Position of the Kidneys
•
Kidneys supported by three layers of supportive tissue
•
The renal capsule adheres directly to the kidney surface and isolates it from surrounding
region
•
Position of the Kidneys
•
The adipose capsule attaches the kidney to the posterior body wall and cushions it against
trauma
•
Position of the Kidneys
•
The renal fascia is dense fibrous connective tissue which surrounds the kidney and
anchors these organs to the surrounding structures
•
Internal Anatomy
•
The kidney has three distinct regions
–
Cortex
–
Medulla
–
Pelvis
–
Internal Anatomy
•
The most superficial region
•
The renal cortex is light in color and has a granular appearance
•
Internal Anatomy
•
Deep to the cortex is the renal medulla
•
Darker tissue which exhibits cone shaped tissue masses called medullary or renal
pyramids
•
Internal Anatomy
•
Each renal pyramid has a base which is convex, and a apex which tapers toward its apex
or papilla
•
Internal Anatomy
•
The apex, or papilla, points internally
•
The pyramids appear striped because they are formed almost entirely of roughly parallel
bundles of urine collecting tubules
•
Internal Anatomy
•
Inward extensions of cortical tissue called renal columns separate the pyramids
•
Each medullary pyramid is surrounded by a capsule of cortical tissue to form a lobe
•
Internal Anatomy
•
Within the renal sinus is the renal pelvis
•
This flat, funnel shaped tube is continuous with the ureter leaving the hilus
•
Internal Anatomy
•
Branching extensions of the renal pelvis form 2-3 major calyces, each of which subdivides to form several minor calyces
•
These cup shaped areas collect the urine which drain continuously from the papillae
•
Internal Anatomy
•
Urine flows through the renal pelvis into the ureter, which transports it to the bladder
•
The walls of the calyces, pelvis, and ureter contain smooth muscle which contract to
move urine
•
Blood Supply
•
The kidney continuously cleanse the blood and adjust its composition
•
Kidneys possess an extensive blood supply
•
Under normal resting conditions, the renal arteries deliver approximately one-fourth of
the total systemic cardiac output (1200 ml) to the kidneys each minute
•
Blood Supply
•
The renal arteries issue at right angles from the abdominal aorta
•
Each renal artery divides into five segmental arteries that enter the hilus
•
Each segmental artery divides into lobar and interlobar arteries
•
Anatomy of the Kidneys
•
The main structural and functional unit of the kidneys is the uriniferous tubule
•
The unit consists of a nephron and its collecting duct or tubule
•
Anatomy of the Kidneys
•
Uriniferous tubules are separated from one another by small amounts of loose areolar
connective called interstitial connective tissue
•
Anatomy of the Kidneys
•
The urine forming nephron is composed of
•
–
Renal corpuscle
–
Proximal convoluted tubule
–
Loop of Henle
–
Distal convoluted tubule
A collecting duct (collecting tubule)
–
Concentrating urine
•
Anatomy of the Kidneys
•
Throughout its length the uriniferous tubule is lined by a simple squamous epithelium
that is adapted for various aspects of the production of urine
•
Mechanisms of Urine Production
•
The uriniferous tubule produces urine through three interacting mechanisms
–
Filtration
–
Reabsorption
–
Secretion
•
Mechanisms of Urine Production
•
In filtration a filtrate of the blood leaves the kidney capillaries and enters the nephron
•
This filtrate resembles tissue fluid in that it contains all the small molecules of blood
plasma
•
Mechanisms of Urine Production
•
As filtrate proceeds through the uriniferous tubule, the filtrate is processed into urine by
the mechanisms of reabsorption and secretion
•
Mechanisms of Urine Production
•
During reabsorption, most of the nutrients, water, and essential ions are reclaimed from
the filtrate, and returned to the blood of capillaries in the surrounding connective tissue
•
99% of the volume of renal filtrate is reabsorbed
•
Mechanisms of Urine Production
•
As the essential molecules are reclaimed from the filtrate, the remaining wastes and
needed substances contribute to the urine that ultimately leaves the body
•
A passive process
•
Mechanisms of Urine Production
•
Secretion is an active process which moves undesirable molecules into the tubule from
the blood of surrounding capillaries
•
Nephrons
•
Each kidney contains over 1 million tiny blood processing units called nephrons, which
carry out the processes that form urine
•
In addition, there are thousands of collecting ducts, each of which collects urine from
several nephrons and conveys it to the renal pelvis
•
Nephron - Renal Corpuscle
•
The first part of the nephron, where the filtration occur, is the spherical renal corpuscle
Nephron - Renal Corpuscle
•
Renal corpuscles consist of a tuft of capillaries called a glomerulus surrounded by a cup
shaped, hollow glomerular capsule (Bowman’s capsule)
•
Nephron - Renal Corpuscle
•
The glomerulus lies in the glomerular capsule like an under inflated ballon
•
This tuft of capillaries is supplied by an afferent arteriole and drained by an efferent
arteriole
•
Nephron - Renal Corpuscle
•
The endothelium of the capillaries in the glomerulus is fenestrated (pores) and thus these
capillaries are highly porous, allowing large quantities of fluid and small molecules to
pass from the capillary blood
•
Nephron - Renal Corpuscle
•
The fluid passes from the capillary into the hollow interior of the glomerular capsule, the
capsular space
•
This fluid is the filtrate that is ultimately processed into urine
•
20% enters the space while 80% remains in the blood within the capillary
•
Nephron - Renal Corpuscle
•
The external parietal layer of the glomerular capsule, which is simple squamous
epithelium, simply contributes to the structure of the capsule
•
It plays no part in the formation of filtrate
•
Nephron - Renal Corpuscle
•
The capsule’s visceral layer clings to the glomerulus and consists of unusual, branching
epithelial cells called podocytes
•
Nephron - Renal Corpuscle
•
The podocytes have many branches which end in foot processes or pedicels
•
The processes inter digitate with one another as they surround the glomerular capillaries
•
The filtrate passes through the thin filtration slits into the capsular space
•
Nephron - Renal Corpuscle
•
The external parietal layer of the glomerular capsule, which is simple squamous
epithelium, simply contributes to the structure of the capsule
•
It plays no part in the formation of filtrate
•
Nephron - Renal Corpuscle
•
The external parietal layer of the glomerular capsule, which is simple squamous
epithelium, simply contributes to the structure of the capsule
•
It plays no part in the formation of filtrate
•
Nephron
•
Each nephron consists of a glomerulus, a tuft of capillaries associated with a renal tubule
•
The end of the renal tubule is a blind, enlarged, and cup-shaped and completely surround
the glomerulus
•
Nephron
•
The renal corpuscle refers to the enclosed glomerulus and the capsule of the glomerulus
referred to as Bowman’s capsule
•
Nephron
•
The glomerulus endothelium is fenestrated, (penetrated by many pores), which make
these capillaries exceptionally porous
•
The capillaries allow large amounts of solute-rich, virtually protein free fluid to pass from
the blood into the glomerulus capsule
•
This plasma-derived fluid or filtrate is the raw material that is processed by the renal
tubules to form urine
•
Nephron
•
Nephron
•
The external parietal layer of the glomerular capsule is simple squamous epithelium
•
This layers contributes to the structure of the capsule and plays no part in forming filtrate
•
The visceral layer that clings to the glomerulus consists of highly modified, branching
epithelial cells called podocytes
•
Nephrons
•
Podocytes terminate in foot processes, which intertwine and form filtration silts or slit
pores
•
The silts allow filtrate to pass to the interior of capsule
•
Nephrons
•
The filtration membrane is the actual filter that lies between the blood and the interior of
the glomerular capsule
•
It is a porous membrane that allows free passage of water and solutes
•
Nephrons
•
It is a porous membrane that allows free passage of water and solutes smaller that plasma
proteins
•
The capillary pores prevent passage of blood cells, but plasma components are allowed to
pass
•
Nephron
•
Once filtered out of the plasma the urine enters the collecting duct
•
Urine passes into larger ducts until it reaches the ureters
•
It leaves the kidneys and moves toward the bladder in the ureters
------------------------------------------------------------------------------------------------------------