Human Arterial System

 

 Human Arterial system :

consists of two main arteries :

1. pulmonary artery and

2. Aorta

pulmonary artery :

Arises from top Left  region of Rt. ventricle and divides into two branches : Rt. pulmonary artery and Lt. pulmonany artery. Rt- Pulmonary artery Carry deoxygenated blood to Rt lungs. Lt. pulmonary artery Carry deoxygenated blood to Lt lungs.

 

Aorta: Arises from top right region of left ventricle It ascends, get curved towards left and descends down. thus, it has ascending aorta, arc of aorta and descending aorta.

The ascending aorta gives a pair of coronary artery inside pericardium to the wall heart.

 

- Arc of aorta gives 3 arteries -

Branchiocephalic artery , Lt. Common Carotid artery and Lt. subclavian artery.

Branchiocephalic artery : divides into two branches : Rt common Carotid artery and Rt subclavian artery

Rt. common Carotid artery : divides into Rt. internal Carotid artery and Rt. External Carotid artery.

R t. internal Carotid artery supplies blood to Brain ( Neural artery), Eye ( opthalmic artery) , Nose (nasal artery) precephalic artery to parts of head.

 

Rt. external Carotid artery supplies blood to superficial parts of head by following arteries:

• Superior thyroid artery - to thyroid gland and adjacent muscles.

• Facial artery to facial parts of head.

• occipital artery to occipute part of head.

• temporal artery to temporal frontal and Parietal parts of head.

• Lingual artery to tongue.

• Mandibular artery to lower Jaw.

• Maxillary artery to upper jaw

 

Rt. Subclavian artery - divides into two main branches:

vertebral artery and Auxilliary artery.

• vertebral artery: supplies blood to shoulder region and move towards head from the side of neck and Supplies blood to neck and brain.

  Rt. Axillary artery: supplies blood to scapular region and then enter inside forelimb as branchial artery at lower margin of teres major muscle.

Branchial artery supplies blood to arm region and divides into

radial and ulnar artery at the region of elbow.

the radial and ulnar arteries remain connected with each other by deep and superficial palmar arches at the region of palm from these palmar arches, the palmar arteries and arises supplies blood to palm and fingers.

 

Lt. Common Carotid artery: As in Rt. Common Carotid artery.

Lt. Subclavian artery: As in Rt. Subclavian artery.

Blood supply to Brain:

The terminal branches of two internal Carotid artery and two vertebral artery [ Basilar arteries] enter inside cranium and they form anastomosis [ interconnections of arteries] which is a circular structure and called Circle of willi or willi's Circle.

Three arteries; Anterior Cephalic, middle Cephalic and posterior cephalic arises from Circle of willi and supplies blood to brain.

 

Aorta descends and runs mid-dorsally up to posterior end of body. In thoracic region aorta gives following paired arteries.

- Oesophageal arteries to oesophagus.

- Bronchial arteries to bronchus.

- Inter coastal arteries to intercostal muscles.

- superior phrenic arteries to diaphragm.

 

Aorta penetrates diaphragm and enters inside abdominal cavity and gives following arteries:

- A pair of inferior phrenic arteries to diaphragm.

- A single Coeliac artery in It. side which divides into hepatic artery to liver and gastric artery to stomach, spleen and pancreas .

- Anterior mesenteric artery to small intestine.

- A pair of renal arteries to kidney. from each renal artery a supra renal artery arises and supply blood to adrenal gland.

 - A pair of gonadial artery to gonads.

- Posterior mesenteric artery to rectum and large intestine

- Four pairs of lumbar arteries to muscles of abdominal wall.

- At posterior end of body Aorta bifurcates into common iliac arteries.

Each common iliac artery divides into internal iliac artery and external iliac artery

Internal iliac artery supplies blood to organs of pelvic region urinary bladder, uterus, anus etc.

External iliac artery enters inside hindlimb of own side as femoral artery to supply blood to back side of thigh.

At the region of Knee it is Called popliteal artery which divides into anterior tibial artery and posterior tibial artery and supplies blood to leg.

* Coccygeal artery supplies blood to Coccyx.

* vasa vasorum supplies blood to blood vessels.

* Vasa Nervourum supplies blood to nerves.

* In liver 80% blood supply by hepatic portal vein and 20% supply by hepatic artery.

 

 

 

 

 

 

 

 

 

Human Excretory System: Urine and Micturition

 Urine and micturition

urine is liquid and Consists of 96% - water, 2 % urea, 2% other substances. Other substances includes organic and inorganic Substances like Uric acid, creatinine, Hippuric acid, Na, K, Ca, Mg, Chloride etc.

About 1.5 to 2  ltrs urine is formed each day. It is transparent light yellow coloured due to pigment urochrome.

PH =6 but depends upon diet and ranges from 5 to 7.5.

specific gravity: 1.003 to 1.040

It has faint aromatic smell due to urinods. If allowed to stand, urea Changes into ammonia by bacterial action and gives strong pungent smell.

Amount of urine depends upon:

* Fluid intake: when fluid intake  is more , more urine is formed and when fluid intake is low less urine is formed.

* Environmental Condition: when temperature is high less amount of urine is formed and when temperature is low more amount of urine is formed.

* Physical activity: During more physical activity less amount of urine is formed as blood flow to Kidney is less and during less Physical activity more urine is formed.

* Intake of diuretics: Diuretics like tea, coffee, alcohol etc decreases ADH Production. thus, more urine is formed.

Micturition: also called urination. The act of voiding (passing out) urine is  called urination or micturition.

when about 300ml urine get accumulated in the bladder the urge of micturition is felt. At this time, the transitional epithelium starts to stretch and is detected by stretch receptors and the micturition reflex operates. the detrusor muscles contracts and internal urethral sphincter opens and sense of urination begins. The external urethral sphincter is voluntary and regulated by higher inhibitory Centre of brain. thus, the act of micturition Can be prolonged to some extent. parasympathetic nerves Contracts detrusor muscles and relaxes internal urethral sphincter while sympathetic nerves relaxes detrusor muscles and Contracts internal urethral sphincter.

Human Excretory System : Counter current Mechanism

 

Counter Current Mechanism

The countercurrent mechanism is a  process that occurs in the kidneys, enabling them to concentrate urine and maintain water and electrolyte balance in the body. It primarily takes place in the loop of Henle, and involves the countercurrent multiplier system in the loop of Henle and the countercurrent exchanger in the vasa  recta (the parallel network of capillaries around LOH).

Mammals have the ability to produce concentrated urine.

The Henle's loop and vasa recta play a significant role in this.

The flow of filtrate in the two limbs of Henle's loop is in opposite directions and thus forms a counter current.

Large amount of Na+ ions are actively reabsorbed from filtrate into interstitium in ascending limb of loop of Henle and is followed by Passive transport of CI-. this increases osmolarity of medulla region. Thus,  more water is reabsorbed from DLOH and more hypertonic nephric filtrate reaches in ascending limb. Thus, more Na+ is reabsorbed from ALOH. which further increases osmolarity of interstitium of medulla. Thus, LOH acts as counter Current multiplier.

The flow of blood through the two limbs of the vasa recta is also in a countercurrent pattern i.e.  in opposite direction. only about ( 1-2)% of total  renal blood flows through vasa recta. the descending Vasa recta lies in close aproximity with ascending limb of loop of Henle and receives some Na+ and CI- while ascending vasa recta is in Close aproximity with descending limb of loop of Henle and leaves  Na+ and CI- in the interestitium. Thus, it acts as Counter current exchanger.

The proximity between the  Henle’s loop and vasa recta, as well as the countercurrent in them help in maintaining an increasing osmolarity towards the inner medullary interstitium, i.e., from 300 mosmol/L  in the cortex to about 1200 mosmol/L  in the inner medulla.

This gradient is mainly caused by NaCl and urea.  NaCl is transported by the ascending limb of Henle's loop which is exchanged with the descending limb of vasa recta. NaCl is returned to the interstitium by ascending part of the vasa recta. 

The filtrate is concentrated as it moves down the descending limb but is diluted by the ascending limb.  DCT & collecting duct concentrate the filtrate about four times, i.e., from 300 mOsmol/L  to 1200 mOsmol/L  an excellent mechanism of conservation of water. 

Similarly, small amounts of urea/electrolyte enter the thin segment of the ascending limb of Henle’s loop which is transported back to the interstitium by the distal region of collecting duct.  This special arrangement of Henle's loop and vasa recta is called the countercurrent mechanism.

This mechanism helps to maintain a concentration gradient in the medullary interstitium.  Presence of such interstitial gradient helps in an easy passage of water from collecting  ducts.

As the filtrate flows down in the collecting duct  more and more water moves out of the tubule by osmosis which makes filtrate hypertonic to blood.

The human kidney can produce urine nearly four times more concentrated than the initial filtrate formed.

Human Excretory System: Mechanism of urine formation

 

Mechanism of urine formation or Process of urine formation:

The process of formation of   Urine is called Uropoiesis. It takes place in nephron. Each nephron is independent and Can Produce miniscule amount of urine. This process gets completed in 3 steps; Ultrafiltration, selective reabsorption and tubular secretion.

• Ultrafiltration: It is process in which blood is filtered under pressure in malphigian body of nephron.

The main driving pressure for it is hydrostatic pressure of blood in glomerulus (A) which is about (60-70) mmHg. However, this pressure is opposed by osmotic pressure of plasma protein or Blood Colloidal osmotic pressure (B) which is about 30mmHg and also opposed by capsular hydrostatic pressure or hydrostatic pressure of nephric filtrate in Cavity of Bowmans Capsule (C) which is about 20 mmHg.

Thus, the net filtration pressure (NFP) = A - (B+C)

= (60 to 70) - ( 30+20) = (60 to 70) - 50 = 10 to 20

Thus, 10 to 20 mmHg pressure is responsible for

 Ultrafiltration.

During this process, blood has to pass through endothelium, basement membrane and squamous Cells of visceral layer of Bowman's Capsule. out of these 3 layers, basement membrane acts as filter.

The filtrate passes into Capsular space (Cavity of Bowman's Capsule) and is Called nephric filtrate which is preliminary form of  urine.

The nephric filtrate Contains all the substances in blood except blood cells and plasma protein.

Nephric filtrate= Blood - (Blood Cells+ plasma protein) or

Nephric filtrate= plasma - plasma protein

About 125ml nephric filtrate is produced in a minute. Thus, about 180 ltrs nephric filtrate is produced perday. This is Called glomerular filtration rate(GFR).

• Selective reabsorption: out of 180 ltrs of nephric filtrate only about 1.5 to 2 Ifrs get changed into Urine while other about 178 ltrs amount is reabsorbed in tubule. This process is Called Selective reabsorption. All the useful substances present in nephric filtrate are reabsorbed by this process.

In PCT : most of the substances are reabsorbed in PCT. All most all glucose, amino acids, hormones & vitamins are reabsorbed. About (70 to 80)% Na+, CI-, K+, H2O etc. are reabsorbed. some amount of urea is also reabsorbed.

substances are reabsorbed by Active transport and passive transport. Glucose, amino acids, vitamins, hormones, Na+ , K+ etc are actively reabsorbed by using energy even against concentration gradient. water, CI- etc are passively reabsorbed by diffusion.

Maximum reabsorption takes place in PCT.

In PCT , nephric filtrate is isotonic.

In DLOH: As the nephric filtrate moves down in DLOH, water is reabsorbed as it is permeable to water. Thus, filtrate become more and more hypertonic as it moves in DLOH.

In ALOH: As the nephric filtrate moves in ALOH, Na+,  CI- , k+ etc are actively reabsorbed. Thus, filtrate become more and more hypotonic as it moves in ALOH.

At same level of DLOH and ALOH, filtrate is hypertonic in DLOH.

 In LOH, 25% of filtered ions and 20% of filtered water is reabsorbed. 

Minimum reabsorption takes place in ALOH.

• In DCT: Absorption of water and salts takes place under the influence of hormones ADH and Aldosteron respectively. the absorption depends upon amount of water and Salt present in body. thus, it is facultative reabsorption.

In Collecting duct reabsorption of water takes Place and is regulated by hormone ADH. At distal Part of Collecting duct reabsorption of Urea abo takes place which is Secreted into tubule in thin part of ascending limb of loop of Henle. This helps to increase the osmolarity of medulla and it is Called Urea recycling.

 • Tubular secretion: It is just reverse Process of selective reabsorption. In it; some harmful substances present in blood are secreted into tubule. It takes place in PCT and DCT along with selective reabsorption. The substances like 

H+ ions, K+ ions, Hippuric acid, Creatinine , uric acid etc. are passed into tubule.

In DCT, exchange of Na+ and K+ ions takes place in which Na+ ions in nephric filtrate is reabsorbed from tubule and K+ ions in blood Passes into tubule.

At the end of these 3 processes Urine is formed.

Human Excretory System: Excretory Organs

 

The process of formation of urine, its transformation, its temporary storage and its elimination from body form a system Called urinary system which is commonly Called excretory system. It Consists of kidneys, ureter, urinary bladder and urethra.

Human Circulatory system

Click to view the file Human Circulatory System

Regulation of respiration

 Respiration is involuntary process and is regulated by Nervous system and Some Chemicals in blood.

The voluntary regulation is done by higher Centres in cerebrum while involuntary regulation is of two types: Nervous regulation and chemical regulation.