Download The structure of Kidney

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Digestion,Absorption and Use of Food
Nutrients are used by the cells as an energy source. This energy is used for metabolic
activities, growth and repair of tissues.
Nutrients are usually too large to pass through the cell membranes. Thus, organisms
must break down their foodstuffs into their components for passing through the cell
membrane.
All animals and human are the heterotrophic organisms that obtain their food from
autotrophs.
Plants are the autotrophic organisms that produce their own food.
The alimentary canal
İt is a long tube which start from mouth and with anus.
Food is digested in the alimentary canal, the soluble products are absorbed and the
indigestible residues expelled.
The structure of alimentary canal
1- Mucosa layer: The inside of the alimentary canal is lined by layers of Epithelium
cells
The functions of Epithelium cells
a) they produce new cells
b) Some of them can produce MUCUS.
MUCUS: It is a slimy liquid that lubricates the lining of the canal and protects it from
wear and tear, mucus may also protect the lining from attack by the digestive
enzymes.
c) Some epithelium cells produce digestive enzymes
Such as; in the stomach and small intestinal lining.
2- Submucosa layer : This layer is rich in blood capillaries
3- Muscularis: In this layer there are two main kinds of muscles which are;
a)Circular muscle: the fibres of circular muscle run round the canal
b) Longitudinal muscle: The fibres of longitudinal muscle run along the alimentary
canal.
Foodstuffs can be divided into six groups:
Carbohydrates
Minerals
Lipids
Vitamins
Proteins
Water
Carbohydrates, lipids and proteins are large food molecules, so that they need digestion
Vitamins, water, and minerals may enter the blood vessels without digestion
STEPS IN DIGESTION
1-Mechanical digestion (INGESTION):
It is the breaking down the big food molecules into their smaller pieces by the aid of
teeth, tongue, and saliva.
2-Chemical Digestion.
It is the breaking down the food molecules into their smallest unit by the aid of enzymes
and water.
4-Absorption:
Smallest units of foods can pass through the epithelium of alimentary canaland enter the
blood vessels. Blood transports the absorbed nutrients to cells.
HUMAN DIGESTIVE SYSTEM
Human digestive system has two parts
1) Alimentary canal
2) The accessory organs
The major organs of your alimentary canal (digestive tract)
1- Mouth
2- Esophagus (glottis)
3- Stomach
4- Small intestine
5- Large intestine (colon and rectum)
Food passes throuhg alll of these organs.
The accessory organs are The tongue, teeth, salivary glands, liver, gallbladder, and
pancreas.
Although food doesn`t pass through them, they are important in mechanical and
chemical digestion.
Digestive Enzymes
- Some of the digestive enzymes are produced by epithelial cells in the lining of
the alimentary canal such as stomach and small intestinal lining
- Others are produced by glands such as salivary glands pancreas produce
enzymes and pour them through tubes into the alimentary canal.
1)
Alimentary canal
a) The Mouth
Mechanical and chemical digestion begin in your
mouth. Food is ingested using the teeth, lips and
tongue. The teeth then bite or grind the food into
smalle pieces. The tongue mixes the food with
saliva and form of it into a bolus The bolus is
then swallowed.
SWALLOWING
1) Tongue move upward and forcing the bolus to the back of the mouth.
2) The soft palate closes the nasal cavity at the back.
3) Epiglottis automatically covers the opening to the windpipe to prevent food
(bolus) from entering it, otherwise you would choke.
b) Esophagus
It is a muscular tube about 25cm long. No
digestion takes place in the esophagus.
The wall of the tube contains circular and
longitudinal muscles which conract and relax
to make food move down. These waves of
muscle contraction, called Peristalsis, move
food through the entire digestive tract.
c)
STOMACH
The structure of Stomach
 The entrance of stomach is normally closed by a
ring of muscle at the lower end of the esophagu
and Stomach also is connected with the small
intestine by a lower opening called pyloric
sphincter.

The stomach has strong, elastic, muscular walls.
Circular muscles provide horizontal movement of
stomach.
Longitudinal muscles provide upward and
downward movements of stomach.
Inner layer of stomach has a wrinkled
appearance. The millions of gastric glands are
located in the mucosal layer. Gastric glands
Produce gastric juice containing HCL acid,
pepsinogen, and Mucus.
Mucus protects the stomach from strong digestive
solution.
Pepsinogen inactive form of Pepsin, and Pepsinogen is converted to pepsin by HCI
acid.

Functions of stomach:
It stores ingested food.
It produces gastric juice to continue the digestion of food.
It mixes the digestive juices and food by physical movements
SMALL INTESTINE:
Small intestine is located between stomach and large intestine. Digestion of food is
completed in the small intestine and nutrients are absorbed through its wall.
The structure of Small intestine
 Different part of small intestine has different name; the first part, nearest the
stomach is the duodenum, the part nearest to the colon is the ileum.
1- Duodenum:
Most of the chemical digestion takes place in the duodenum.
Liver and pancreas give their secretion to duodenum by duct.
2-ileum

The lining of the small intestine appears velvety because of the millions of tiny
finger-like projections called villi. These structures increase the surface area of
small intestine (about 600 times)

If the lining of intestine was smooth like
the inside of water pipe, food would
move rapidly through the intestine and
many valuable nutrients would not be
absorbed.
Villi;
They are tiny finger like projections
which are located internal surface of the
small intestine.
They resist the food movement to
complete its digestion and contain blood
capillaries transporting digested sugars
and
proteins.
Also
they
contain
lymphatic vessels transport the digested fats.
DIGESTIVE SECRETIONS:
Digestive secretions originate from;
Salivary glands. Gastric glands. Pancreas. Liver-Gall bladder. Small intestine.
The Secretion of MOUTH:
There are three pairs of salivary glands in the lining of the mouth. Salivary glands
secrete saliva into the mouth. Saliva contains salivary amylase (sometimes called
ptyalin enzyme) which converts
the carbohydrates (e.g.starch) into disaccharides
(e.g.maltose) .
The Secretion of STOMACH:
The millions of gastric glands are located in the inner layer of stomach.
Gastric glands produce Gastric juice.
Gastric juice contains hydrochloric acid and pepsin enzyme and Mucus
Functions of HCL; HCL destroys the most micro organisms which are entering the
stomach and it provides the best degree of acidity for pepsin to work in.
Function of pepsin enzyme; Pepsin is a protease (or proteinase), it acts on proteins
and breaks them down into soluble compounds called peptides
Pepsinogen is the inactive form of Pepsin; it will be active in the presence of HCL.
Function of Mucus: The lining of the stomach is protected from the action of pepsin and
HCI acid by the layer of Mucus.
The Secretion of Small Intestine:
The digestion of all foodstuffs is completed at the small intestine. Small intestine secretes
following enzymes;
Enterokinase: Converts the trypsinogen to Trypsin.
Proteinase: breaks down the polypeptides to aminoacids.
Sucrase; acts on sucrose.
Maltase; acts on maltose
Lactase; acts on lactose.
The Secretion of Liver :
Liver cells secrete bile.
Bile is a green, watery fluid made in the liver, stored in the gall bladder
Gall bladder is a sac connected with liver by the liver-bile duct and it is located behind
the right lobe of the liver. Its function is
Bile also contains bile salts which act on fats rather like a detergent.They help the
digestion of fatty materials by breaking them into small pieces.
Pancreatic secretions:
Pancreas is a digestive gland lying below the stomach and is connected with duedonum
by pancreatic duct.
Pancreas secretes following enzymes;
Lipase; acts on fats
Pancreatic Amylase; acts on carbohydrates
There are several proteases which break down proteins to peptides and amino acids for
example; trypsin one of the proteases from the pancreas, is secreted as the inactive
trypsinogen and is activated by Enterokinase,
Trypsin acts on proteins
DIGESTION OF CARBOHYDRATES
Digestion of Carbohydrates in MOUTH
Chemical digestion of carbohydrate starts in mouth.
Salivary glands secrete saliva into the mouth. Saliva is a juice which contains digestive
enzyme called salivary amylase. Amylase acts on cooked starch and begins to break it
down into maltose.
Starch + Water Amylase
Maltose
Digestion of Carbohydrates in STOMACH
Stomach is an acidic area. Amylase can not work in acidic region. Therefore, chemical
digestion of carbohydrates stop in stomach.
Digestion of Carbohydrates in SMALL INTESTINE
When food passes into the small intestine from stomach, it stimulates the cells of
duodenum.
Then, Secretin hormone is released into the blood from cells in the duodenum.
When secretin reaches the pancreas it stimulates the pancreas to produce pancreatic
juice.
Pancreatic juice contains several enzymes and hydrogencarbonate which partly
neutralizes the acid liquid from the the stomach. This is necessary because the enzymes
of the pancreas and small intestine do not work well in acid conditions.
Enzymes act on every types of carbohydrates.
Starch + H2O Pancreatic amylase
Maltose + H2O maltase
Sucrose + H2O sucrase
Maltose (disaccharide)
Glucose + Glucose
Glucose + Fructose
Lactose + H2O lactase
Glucose+ Galactose
Digestion of carbohydrates is completed in small intestine.
Digestion of PROTEINS
In Stomach
Protein molecules must be broken down to individual amino acids in order to be
absorbed.
The digestion of proteins begins in the stomach, with the secretion of gastric juice.
When the food reaches the stomach it stimulates the stomach lining to produce a
hormone called gastrin. This hormone circulates in the blood and, when it returns to
the stomach in the bloodstream, it stimulates the gastric glandsto secrete gastric
juice
Gastric juice containing the pepsin enzyme;
Pepsin is a protease (or proteinase), it acts on proteins and breaks them down into
soluble compounds called peptides
PROTEINS Pepsin peptons (peptides)
in Small Intestine
Tripsinogen and other proteinases take role in the digestion of proteins that are secreted
by pancreas.
Enterocinase secreted by intestinal glands to activate Trypsinogen to trypsin.
Tripsinogen + Enterokinase -------------- Tripsin
Peptones+H2O Tripsin Peptides + Amino acids
Peptides+ H2O Proteinases aa + aa + aa + aa +… (aa = amino acid)
Digestion of LIPIDS
Digestion of lipid occurs only in small intestine.
The cells of the liver produce bile. Then, it is stored in gall bladder.
When food enters to small intestine,
Bile does not contain enzyme but it aids mechanical digestion of lipid. This process is
called emulsification.
Lipid bile Small lipid particles
Lipase is secreted from pancreas. Lipase breaks down lipid molecules into fatty acids and
glycerol.
Lipid + H2O Lipase
3 Fatty acid + Glycerol
ABSORPTION
There are many finger like projections in the lining of small intestine.They are called
VILLI.
Villi increa the absorption surface of small intestine.
Passing of digested materials from small intestine to blood is called absorption.
Vitamins and inorganic materials pass into the blood without digestion.
Glucose, amino acids and vitamins are absorbed by blood capillaries via epithelial cells.
They are then carried away in capillaries, which join up to form veins. These veins unite
to formone large vein , the hepatic portal vein
This vein carries all the blood from intestine to the liver, which may store or alter any of
the digestion products. When the products are released from the liver, they enter the
general blood circulation
Fatty acids and glycerol combined to form fats again in the intestinal epithelium. These
fats then pass into the lymphatic system which forms a network all over the body and
eventually emptiesits contents into the bloodstream.
The blood will transport the digested simple food materials to body cells then,body cells take
their requirements from blood.
Large Intestine
It is the final part of the digestive tract
The large intestine consists of the following parts:
1. Caecum and appendix:
It is a closed sac-like structure located in the beginning of
the large intestine. In humans, appendix and caecum are
small structure, possibly without digestive function. The
appendix, however, contains lymphoid tissue and may
have an immunological function.
2. Colon: It is starts after the caecum The colon is
divided into three parts
Ascending colon
The transverse colon
The descending colon
3. Rectum:
It is a straight tube, which is located behind the bladder.
The Function of Large Intestine
1-Water absorption will occur in the large intestine.
2- Bile salts are absorbed and returned to the liver by the blood circulation
3-Keeping the waste material for a limited time, until it is excreted in suitable time.
4-The semi-solid waste, the faeces or stool is passed into the rectum by peristalsis and is
expelled through anus.
Use of digested food
1- Glucose:
During respiration in the cells, glucose is oxidized to carbon dioxide and water. This reaction
provides energy for cells
2- Fats:
These are built into cell membrane and other cell structure. Fats also form an important source
of energy for cell metabolism. Fats can provide twice as much energy as sugars.
3- Amino acids
These are absorbed by the cells and built up, with the aid of enzymes, into proteins
a) Some of the proteins will become plasma proteins in the blood
b) Others may form structures such as the cell membrane or
c) They may become enzymes which control the chemical activity within the cell.
Storage of digested food
If more food is taken in than the body needs for energy or for building tissues, it is stored in
one of the following ways
Glucose
Excess amount of Glucose changes to Glycogen in Liver
Some of the glycogen store in the liver and the rest in the muscles.
Fat
The fat is stored in adipose tissue in the abdomen, round the kidney and under the skin.
These are the fat depots
Amino acids
Amino acids are not stored in the body; those are not used in protein formation are
deaminated.
Excess amino acids are converted to glycogen in the liver. During this process, amino part of
the amino acid is removed and changed to UREA which is later excreted by the Kidneys.
The LIVER
İt is a large, reddish- brown organ which lies just beneath the diaphragm and partly
overlaps the stomach.
All the blood from the blood vessels of the alimentary canal passes through the liver.
The functions of LIVER
Liver has more than 500 functions, some of them;
1) Regulation of blood sugar
After a meal, The liver removes excess glucose from the blood and stores it as Glycogen.
Glucose ............Glycogen
In the periods between meals, when the glucose concentration in the blood starts to fall,
the liver converts some of its stored Glycogen into glucose and releases it into the
bloodstream.
In this way, the concentration of sugar, in the blood is kept at a fairly steady level.
2) Production of Bile
Cells in the liver make bile continuously and this is stored in the gall bladder.
The bile contains bile salts which assist the digestion of fats
3) Deamination
Excess amino acids are converted to Glycogen in the liver, During this process, Amino
part of the amino acid is removed and changed to UREA.
When the Amino group is removed from amino acids, it forms Amonia. Amonia is very
poisonous to the body cells, and liver converts it at once to urea (harmless).
4) Storage of IRON
Millions of red blood cells break down every day. The iron from the haemoglobin is stored
in the liver.
5) Manufacture of plasma proteins
The liver makes most of the proteins found in the blood plasma,such as fibronogen (it is
involved in blood clotting)
6) Detoxication
Poisonous compounds are converted to harmless substances, later excreted in the urine.
7) Storage of Vitamins
Liver store fat soluble vitamins; vitamin A and vitamin D
Homeostasis
The maintance of the internal environment within narrow limits is called homeostasis.
Excretory System
Excretion: throw out the metabolic wastes from body which are produced after
cellular activities.
The Eliminations are sometimes confused.
Elimination: Undigested and unabsorbed food materials are eliminated from the body
in the feces. Such substances never participated in the organism’s chemical
metabolism or entered body cells.
FOOD INTAKE
Digestion
Undigested food
Absorption
Utilization of nutrients by cells
Metabolic wastes
EXCRETION





ELIMINATION AS FECES
The functions of Excretory System:
Filtration and excretion of toxic wastes in the blood produced by the metabolic
reactions of cells.
The maintenance of homeostasis by the balance of water and ionic content of the
blood and tissue fluid.
The regulation of blood content.
The regulation of blood PH.
The regulation of blood glucose level.
The principal metabolic waste products are;
1. Water ( H2O )
2. Carbon dioxide ( CO2 )
3. Nitrogenous wastes ( Ammonia, Urea, Uric Acid )
(a) Water and Carbon dioxide (H2O, CO2)
- They are generated during the catabolism of carbohydrates and Lipids.
Excreted by → Lungs, Kidney, and SWEATING.
(b) Nitrogenous wastes:
*Ammonia (NH3)
Amino acids and Nucleic acids contain Nitrogen.
During the breakdown of amino acids, the nitrogen containing amino group is
removed (deamination) and converted to Ammonia.
- Ammonia is highly toxic; some aquatic animals excrete it into the surrounding
water.
* Uric Acid:
Uric acid is produced both from ammonia and by the breakdown of nucleotides
from nucleic
acids. Uric acid forms crystals.
Uric acid can be excreted as a crystalline paste with little fluid loss.
Exp: Insects, certain reptiles, and birds.
* UREA:
Urea is the principal nitrogenous waste product of amphibians and mammals.
It’s produce mainly in the liver.
Urea less toxic than Ammonia.
Urea dissolves in water and is excreted by the Kidney.
THE HUMAN EXCRETORY SYSTEM
The human excretory system composed of:
1. Kidney
2. Urinary tract (URETER)
3. Urinary bladder
4. URETHRA
THE KIDNEY
The kidneys are two bean shaped organs located in the lower thoracic region of
the body.
The structure of Kidney:
- The Kidney composed of four main parts
Renal capsule, Cortex, Medulla and Pelvis.
1) Renal Capsule:
It’s a fibrous layer of connective tissue which surrounds the Kidney.
2) CORTEX:
It’s located below the fibrous coat.
It’s red in color and contains the malpighon bodies (Bowman’s capsule and
glomerulus)
3) MEDULLA:
It’s located below the cortex.
Urinary tracts which drain from the cortex form pyramids.
The tip of each pyramid is a renal papilla.
Each papilla has several pores, the opening of collecting ducts.
As urine is produced it flows through the openings of the collecting ducts, and into
the Renal pelvis.
4) Renal Pelvis:
It forms the innermost portion of the Kidney.
Its function is the collection of urine from the pyramids.
The pelvis transmits the accumulated urine to the Ureter.
THE NEPHRON IS THE FUNCTIONAL UNIT OF THE KIDNEY
Each kidney is made up of more than million functional units called nephron.
Each nephron consists of:
1- Bowman’s Capsule and Glomerulus
2- Proximal Convoluted Tubule
3- Loop of Henle
4- Distal Convoluted Tubule
URINARY TRACT
5- Collecting Duct
1) Bowman’s Capsule:
- Semi-spherical structure
- The inner surface consists of squamous epithelial cells.
2) Glomerulus:
- Blood is delivered to the kidney by the renal artery.
- Small branches of renal artery give rise to efferent arterioles.
- Glomerulus is formed by capillaries from a branch of the efferent renal arteriole.
- The capillaries exit the Bowman’s capsule with the efferent arteriole (Blood
pressure is high in the capillaries of the glomerulus due to its position between two
arterioles)
- These capillaries thicker than other capillaries.
URINARY TRACT:
- After the Malpighian body (Bowman’s capsule & Glomerulus), proximal
convoluted tubule is there, proximal convoluted tubule extends into the loop of
Henle and then into the distal convoluted tubule (the total length approximately
50cm Urinary tract)
- Loop of Henle extends into medulla of kidney.
- Renal artery: It transports blood rich in oxygen and waste.
- Renal Vein: It transports blood is in CO2 with only a small amount of waste.
FILTRATION:
Filtration occurs at the function of the glomerular capillaries and the wall of
Bowman’s capsule.
Blood flows throw the glomerular capillaries under high pressure, forcing more than
10% of the plasma out of the capillaries and pass into the Bowman’s capsule.
Small materials, such as glucose, amino acids, sodium, potassium, chloride,
bicarbonate, and other ions and urea pass through the capillaries into the Bowman’s
capsule, and become part of the FILTRATE.
Blood cells, plasma proteins, and lipid molecules, remain, in capillaries.
- The total volume of blood passing through the kidneys is about 1200ml per
minute.
REABSORPTION: (proximal convoluted tubule)
The simple epithelial cells lining the renal tubule are well adapted for reabsorbing
materials. They have abundant microvilli, which increase the surface area of
reabsorption.
About 65% of the filtrate is reabsorbed as it passes through the proximal
convoluted tubule.
The-proximal convoluted tubule is isotonic to the tissues, its density is equal to that
of the tissue.
Glucose
Amino acids
Vitamins
Other substances of nutritional value are reabsorbed there.
There are many ions including:
- Sodium
- Chloride
- Bicarbonate
- Potassium
LOOP OF HENLE:
Urine is concentrated at the loop of Henle.
- Loop of Henle a structure composed of two parole descending and ascending
arm.
-
The direction of flow in each arm is the reverse of the other Cl ions are
reabsorbed by active transport in the ascending arm Na ions are reabsorbed by
passively reabsorbed.
The concentrated urine then flows to the convoluted tubule.
Distal Convoluted Tubule:
- Water is reabsorbed in this region.
- Its permeability to water is regulated by vasopressin (ADH)
- It’s secreted when the concentration of the blood increases.
- As a result reabsorption of water from the collecting ducts.
Secretion:
Some substances especially potassium, hydrogen and ammonium ions are secreted
from the blood into the filtrate.
Certain drugs such as penicillin are also removed from the blood into the filtrate.
Secretion occurs mainly in the region of the distal convoluted tubule.
Secretions have been retained by the tubules.
Urine is composed of:
98% water
2.5% Nitrogenous wastes (Primarily Urine)
1.5% Salts and traces of other substances such as bile pigments, which may
contribute to the characteristic color.
Urine volume is regulated by the hormone ADH. When are drinks a great deal of
water, the blood becomes diluted and its osmotic pressure
Release of ADH to the pituitary gland, decreases, lessening the amount of water
reabsorbed from the collecting ducts. A large volume of diluted urine is produced.
Sodium reabsorption is regulated by the hormone Aldesterone.
Sodium is the most abundant extra cellular ion, accounting for about 90% of all
positive ions out side cells.
Concentration of sodium is precisely regulated by the hormone ALDESTERONE,
(secreted by the cortex of the adrenal gland).