Physiology No 5

‫بســـم الله الرحمن الرحيم‬

‫المحاضرة‬ ‫الخامسة‬ ‫من صـــفحة ‪ 87‬الى صــفحة‬ ‫‪95‬‬ ‫وصفحة ‪ 98‬الى صفحة ‪105‬‬

Respiratory system * Each cell must acquire O2 & get rid of CO2. * In small animals → exchange of gasses is direct with the external environment. * In complex animals → there is a respiratory system. * Such animals must have a circulatory system to bring O2 & collect CO2. * Aquatic animals use for gas exchange either: 1- Entire body surface e.g. hydras. 2- Gills e.g. fishes. * Insects (& other terrestrial arthropods) have a tracheal system. * Terrestrial vertebrates have lungs. Note: The amphibian ’slungs are not highly developed because . they use their skin for gas exchange To enter the air into the respiratory tract the animals may use: 1- Positive pressure: as in frogs where air is forced into the respiratory tract. Mechanism: *The nostrils are firmly shut, *the floor of the mouth is rised and then *the air is pushed into the lungs. or 2- Negative pressure: as in reptiles, birds & mammals where the lungs are expanded and the air comes rushing in. Gas exchange takes place at exchange area which is highly .vascularized i.e. richly supplied with blood capillaries

Human respiratory system * Air is 50 times richer in O2 if it compared with that in H2O. * In inspiration: airAirtravels from the atmosphere through nasal & oral becomes warmed & takes H O vapor cavities → pharynx → trachea bronchi → bronchioles → alveolar ducts → alveoli where the exchange of O2 & CO2 takes place. 2

@ Trachea & bronchi contain cartilage, lining epithelial cells have cilia and secrete mucous. @ The mucous is continuously transported away from the lungs by the movement of the cilia. This process filters dust particles as air flows in and out of the air passage. When mucous reaches the pharynx we may unconsciously swallow it. @ There are approximately 300 millions alveoli with a total surface area of 85 m2., each alveolar sphere with a diameter of 0.3 mm. @ Efficient gas exchange by diffusion is enhanced by: 1- Extremely thin wall of both alveolar sacs & blood capillaries. 2- Total distance between alveoli & blood capillaries is very short. 3- The dense supply of capillaries in the lungs.

@ The lungs are attached to thoracic cage by the pleura which is a double membrane. @ The pleura consists of: 1- Parietal pleura (outer membrane – fixed to the chest wall). 2- Visceral pleura (inner membrane – fixed to the lungs). @ A thin film of a fluid was found between the 2 membranes which ensures the adhesion between lungs and chest wall in a way that every movement performed by the chest is followed by the lungs. @ Respiratory cycle: It consists of: 1- inspiration. 2- expiration 3- an expiratory pause.

During inspiration: The volume of the chest increases through: 1- Contraction of diaphragm where it descends downwards leading to an increase in the vertical dimension of chest. 2- Contraction of the external intercostal muscles where they elevated the ribs leading to an increase in anteroposterior and bilateral dimensions. The increase in the volume of the chest → an increase in the volume of lungs → a decrease in the pressure in the lungs (-1 mmHg) → rush of atmospheric air into lungs (alveoli) through the respiratory tract till the pressure gradient becomes zero at the end of normal inspiration. Note: During deep inspiration further descend of diaphragm & further elevation of the rib cage through the contraction of a new group of muscles found in the neck region (accessory respiratory muscles).

During expiration: The reverse of inspiration takes place i.e. relaxation of the already contracting muscles where they back to their resting position. Also, during forced expiration: It involves the contraction of the anterior abdomenal muscles which inturn press on the viscera together with upward movement of the diaphragm.

Lung volumes and capacities @ Tidal volume: It is the volume of air inspired and expired during normal quite breathing. It equal 500 ml. @ Inspiratory reserve volume: It is the extra volume of air which can be inspired during deep inspiration over the tidal volume. It equals 3000 ml. @ Exspiratory reserve volume: It is the extra volume of air which can be expired during forced expiration over the tidal volume. It equals 1100 ml. @ Residual volume: It is the volume of air remaining in the lungs after forced expiration (1200 ml). @ Inspiratory capacity: It is the maximum volume of air which can be inspired during deep inspiration after the end of normal expiration. It equals tidal volume (500 ml) + inspiratory reserve volume (3000 ml) = 3500 ml. @ Functional residual capacity: It is the volume of air remaining in the lungs after normal expiration. It equals residual volume (1200 ml) + expiratory reserve volume (1100 ml) = 2300 ml. @ Vital capacity: It is the maximum volume of air which can be expired during forced expiration after deep inspiration. It equals tidal volume (500 ml) + inspiratory reserve volume (3000 ml) + expiratory reserve volume (1100 ml) = 4600 ml. @ Dead space: It is the amount of air contained within the anatomical dead space comprising trachea, bronchi and bronchioles. It equals 150 ml which is always a part of the tidal volume.

Gas exchange Partial pressure of gases

Alveolar air = oxygenated blood (≈arterial blood)

Capillary blood = deoxygenated blood (≈venous blood)

PO PcO

100 mmHg

40 mmHg

40 mmHg

46 mmHg

2

2

Oxygen transport @ Most of O2 found in the blood → oxyhemoglobin. The greater the PO2, the more oxyhemoglobin is formed where arterial blood is 97% saturated with O2. Note: Oxygen-hemoglobin dissociation curve: It is relation between PO2 and the degree of saturation of Hb. @ At the tissues where PO2 is 40 mmHg (or even 15 mmHg during exercise) + increased amount of CO2 + H+ + temperature lead to: Oxyhemoglobin → Hb + O2. Note: The affinity of Hb to CO is 210 times than O2. So, death occurred from CO poisoning. CO2 transport CO2 is transported by blood in 3 forms which are: 1) 7% dissolves in plasma. 2) 23% combines with reduced Hb to form carbaminohemoglobin. 3) In the form of bicarbonate ions (HCO3): where:

RBC H2O

Plasma

os mo s

is Carbonic anhydrase

* CO2

+ H2O

HHb

H+ Hb

O2

H2CO3 Chloride shift phenomenon

HCO3-

Cl-

Excretory system Excretion of nitrogenous wastes

* Once the amino groups have been removed from amino acids (and nucleic acids), they must be excreted from the body in the form of ammonia (as in aquatic invertebrates, bony fishes and amphibian’s larvae), urea (as in adult amphibians and mammals) or uric acid (as in insects, reptiles and birds). * For excretion of nitrogenous wastes there is a primary excretory organ such as: 1- Flame cells as in flatworms. 2- Nephridia as in earthworms. 3- Malpighian tubules as in insects and spiders. 4- Kidneys as in vertebrates.

Human kidneys (an organ of urinary system) Shape & color & size: It is bean shaped, reddish brown, each kidney is about the size of a fest. Location: They located on either side of vertebral column below diaphragm. Each kidney is connected to a ureter. Each ureter carries urine to the urinary bladder where the urine is stored until it go out through urethra. Urethra passes through the penis in male, while it opens ventral to the opening of vagina in .female

Kidney structure In L.S. there are 3 major parts :which are Cortex: Outer layer which has -1 .granular appearance Medulla: It lies on the inner side -2 of the cortex which has a striped appearance. It is arranged in a .group of pyramid-shaped region 3- Pelvis: The innermost part which is a hollow chamber. Urine is collected in the pelvis before entering the is ureter. Each kidney composed of about one million tiny tubules called nephrons.

They are the structural & functional units of the kidney

Renal corpuscle

Nephrons

Proximal convoluted tubule Afferent arteriole Efferent arteriole

Peritubular capillaries

Distal convoluted tubule

Renal arteriole

There are 2 structural classes of nephrons which are: 1- Cortical nephrons: representing 85% of nephrons where almost all the length of which lies within the renal cortex. 2- Juxtamedullary nephrons: representing 15% where their loops of Henle dip deeply into the renal medulla.

Juxtaglomerular apparatus

It is a structure formed when the distal convoluted tubule bends * around to contact the afferent arteriole at the place where it .enters the glomerulus It is composed of specialized tubular epithelial cells of distal * convoluted tubule and the granular cells of the adjacent of the .afferent arteriolar wall * The granular cells secrete an enzyme called renin. This enzyme is responsible for the production of angiotensins, of which angiotensin II. Angiotensin II stimulates the secretion of aldosterone hormone.

Urine formation :Urine formation requires 3 distinct processes which are Glomerular filtration. -1 2- Selective reabsorption. .3- Tubular secretion .Glomerular filtration -1 It takes place between glomerular capillaries endothelium (characterized by the presence of numerous small pores (fenestrations) and Bowman’s capsule (characterized by the presence of podocytes). Podocytes are modified squamous epithelial cells with numerous elongated branches called foot processes which are separated by narrow gaps called filtration slits (slit pores). Fluid and small solutes dissolved in the plasma such as glucose, amino acids, Na, K, Cl, HCO3- , other salts, and urea pass through the membrane and become part of the filtrate. The glomerular membrane hold back blood cells, platelets and most plasma proteins. The filtrate is about 10% of the plasma. The volume of fluid filtered per unite time is called the glomerular filtration rate (GFR). The GFR is about 180 L/day (=125 ml/min.).

Forces affecting the GFR: A)Forces: helping filtration

1- Hydrostatic pressure of the blood inside glomerular capillaries (HPG) (= 50 mmHg) due to: i- The afferent arteriole is 3 times wider than the efferent arteriole ii- The diameter of the renal artery is large in relation to the relelatively small size of the kidney. iii- The renal artery comes directly from the aorta. 2- Colloidal osmotic pressure of the fluid inside the Bowman’s capsule (COPBC). Where the filtrate is free of proteins, so this force normally equals to zero mmHg.

:B) Forces opposing filtration

1- Colloidal osmotic pressure of the glomerular capillary blood (COPG). This pressure is due to plasma proteins and equals 30 mmHg. 2- 1- Hydrostatic pressure of the fluid inside the Bowman’s capsule (HPBC) (= 10 mmHg).

Accordingly,

The net filtering force= The forces helping filtration - The forces opposing filtration = (HPG + COPBC) (COPG + HPBC) = (50 + 0) (30 + 10) = 10 mmHg.

The GFR is proportional to the net filtering force. GFR = Constant x net filtering force. This constant is called filtration coefficient (Kf) and it is equal to 12.5 ml/mmHg/min. i.e. 12.5 ml fluid is filtered for each 1 mmHg net filtering force per 1 min. This coefficient depends on the surface area and the permeability of the glomerular membrane. So, GFR = 12.5 x 10 = 125 ml/min.

Factors affecting GFR 1- Filtration coefficient (Kf). 2- Hydrostatic pressure of the blood inside glomerular capillaries (HPG). 3- Colloidal osmotic pressure of glomerular capillary blood (COPG) 4- Hydrostatic pressure inside the Bowman’s capsule (HPBC). 5- Colloidal osmotic pressure inside the Bowman’s capsule (COPBC).

‫الى‬ ‫اللقــــــــــــــــــ‬ ‫ـاء‬ ‫أ‪ .‬د‪ .‬شــــــبل‬ ‫شـــــــــعلن‬