Human Physiology: A Comprehensive Overview
Posted on May 2, 2024 in Biology
Cardiac Cycles
A cardiac cycle includes all the events associated within one heart beat.
The normal heart beats in healthy adult is 75 beats/min and cardiac cycle last for 0.8 scc.
In the cardine cycle due to the pressure changes atria and ventricles alternately contract and relax, and blood flows from areas of higher blood pressure to areas of lower blood pressure.
• The term systole is used for the contraction and diastole used for the relaxation.
In a normal cardiac cycle, the two atria contract while the two ventricles relax. Then, while the two ventricle contract, the two atria relax.
. Cardiac cycle is described by the following phase:
1) Atrial systole
In this phase Atrial contraction is begins which is last about 0.1 sec at same time ventricle are relaxed.
So, the Right and Left AV valves are open and Atria send blood into the relaxed ventricles,
Atrial systole pushes 25 ml of blood in to ventricles which already contain 105 ml blood so at the end of atrial systole means end of ventricle diastole Ventricles contain maximum blood volume which is 130 ml known as end-diastolic volume (EDV).
In the ECG or EKG it is noted as P wave.
2. Ventricular systole:
■In this phase ventricles begin contraction which is last for 0.3 sec. • Pressure in ventricles rises due to contraction and shut the AV valves which is
heard by “Lubb” Sound.
• For about 0.05 sec all four valve are closed which is known as isovolumetric contraction.
• Ventricular contraction pushes blood out of the ventricles and opens the both Semilunar valve and ejected 70 ml blood in to sorta and same amount of blood in to pulmonary trunk by respectively left and right ventricles so the 60 ml of blood
remains in the each ventricle out of 130 ml. This is known as ventricular ejection which last for 0.25 sec
Ventricular systole isovolumetric contraction + ventricular ejection
-(0.05)+(0.25)
0.3 sec.
Micturition
or urination is the process of emptying urine from the storage organ, namely, the urinary bladder. The detrusor is the smooth or involuntary muscle of the bladder wall. The urethral muscles consist of the external and internal sphincter. The internal sphincter and detrusor muscle are both under autonomic control. The external sphincter, however, is a voluntary muscle under the control of voluntary nerves.
The bladder normally accommodates up to 300- 400 ml in adults. When the bladder is distended it sends signals to the brain, which is perceived as the ‘full bladder’ sensation.
The process of emptying the urine into the urethra is regulated by nervous signals, both from the somatic and the autonomic nervous system. The autonomic nervous system comprises both the sympathetic and the parasympathetic nervous system.
The bladder has two states of function; the storage and emptying phases.
Structure and function of human kidney
■Remove waste products and medicines from the body
■Balance the body’s fluids
■Balance a variety of electrolytes
■Release hormones to control blood pressure
■Release a hormone to control red blood cell production
■Help with bone health by controlling calcium and phosphorus
What is Nephron?
A nephron is the basic structural and functional unit of the kidney. They are the microscopic structure composed of a renal corpuscle and a renal tubule. The word nephron is derived from the Greek word – nephrons, meaning kidney. There are about millions of nephrons in each human kidney.
Structure of Nephron
The mammalian nephron is a long tube-like structure, its length varying from 35-55 mm long. At one end, the tube is closed, folded and expanded, into a double-walled, a cuplike structure called the Bowman’s capsule or renal corpuscular capsule, which encloses a cluster of microscopic blood vessels called the glomerulus. This capsule and glomerulus together constitute the renal corpuscle.
The structure of nephron comprises two major portions:
- Renal Tubule 2. Renal Corpuscle
Renal Tubule
The renal tubule is a long and convoluted structure that emerges from the glomerulus and can be divided into three parts based on function.
• The first part is called the proximal convoluted tubule (PCT) due to its proximity to the glomerulus; it stays in the renal cortex.
• The second part is called the loop of Henle, or nephritic loop because it forms a loop (with descending and ascending limbs) that goes through the renal medulla.
• The third part of the renal tubule is called the distal convoluted tubule (DCT) and this part is also restricted to the renal cortex.
Renal Corpuscle
The renal corpuscle consists of a glomerulus surrounded by a Bowman’s capsule. The glomerulus arises from an afferent arteriole and empties into an efferent arteriole. The smaller diameter of an efferent arteriole helps to maintain high blood pressure in the glomerulus.
The Bowman’s capsule is divided into three layers:
- Outer Parietal layer: It is made up of epithelial cells with minute pores of diameter 12nm.
- Middle Basement membrane: This layer is selectively permeable.
- Inner Visceral Layer: It consists of large nucleated cells called podocytes which bear finger-like projections called podocel.
What is the renin-angiotensin- aldosterone system (RAAS)?
The renin-angiotensin-aldosterone system (RAAS) is the system of hormones, proteins, enzymes and reactions that regulate your blood pressure and blood volume on a long-term basis.
It regulates your blood pressure by increasing sodium (salt) reabsorption, water reabsorption (retention) and vascular tone (the degree to which your blood vessels constrict, or narrow). The RAAS consists of three major substances, including:
- Renin (an enzyme).
- Angiotensin II (a hormone).
- Aldosterone (a hormone).
Enzymes are proteins that help trigger chemical reactions in your body. They build some substances and break others down.
Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, muscles and other tissues. These signals tell your body what to do and when to do it.
What are salivary glands?
Your salivary glands produce saliva (spit) and empty it into your mouth through or small openings. They lubricate your mouth and throat, aid in swallowing and digestion, and help shield your teeth from cavity-causing bacteria.
What are the three major salivary glands?
You have three major pairs of salivary
glands, including your:
Sublingual glands: These are below either side of your tongue, under the floor of your mouth.
Submandibular glands: Located below
your jaw, your submandibular salivary glands consist of two parts: the superficial lobe and the deep lobe. Like your sublingual glands, the saliva produced in your submandibular glands enter your mouth from under your tongue.
Parotid glands: Your parotid glands are just in front of your ears. Similar to your submandibular glands, your parotid glands have two parts: superficial and deep. The saliva produced by your parotid glands enters your mouth from small ducts near your upper molars.
What is the creatinine clearance test?
The creatinine clearance test is a test that checks your how well your kidneys are working. It allows your healthcare provider to see how much creatinine is in a sample of your pee (urine) and blood. The results of this test can lead to a diagnosis of kidney disease.
Creatinine is a waste product of creatine. Creatine is a chemical that your body uses to supply your muscles with energy. As your muscles use energy, they break down. This natural breakdown of muscle tissue causes creatinine to release into your bloodstream Your kidneys typically filter creatinine But, if your kidneys aren’t functioning correctly, you may have higher levels of creatinine in your body than you should.
The creatinine clearance test involves collecting your pee over a 24-hour period and having your blood drawn. Your provider uses these samples to see how much creatinine your kidneys filter over the 24-hour window.
The results of the test show your creatinine clearance. Creatinine clearance is one way to estimate your glomerular filtration rate (GFR), or how well your kidneys are filtering your blood. The GFR is the main number used by your provider to determine how well your kidneys are working.
Healthcare providers don’t use the creatinine clearance test as much as they once did because collecting pee over a 24- hour period is inconvenient. Instead, they usually use a blood test called the estimated glomerular filtration rate (eGFR) coupled with a urine test like urine albumin-creatinine ratio (uACR), which only involves peeing one time.
Composition of lymph
The lymphatic system comprises
Lymph plasma, lymph corpuscles, Lymphold organs
Lymph plasma-
lymph is a interstitial fluid.
It has similar mineral content as in plasma.
Lymph Corpuscles-
Lymph corpuscles refer to the cellular component found in lymph particularly white blood cells.
Lymphoid organs
lymphoid organs are the structure in the body where lymphocytes are produced, stored and even active as a part of the immune system.
Respiratory system
Calculation steps for Total Lung volume/Minute Volume:
1. Tidal volume (VT)
Healthy adult doing 12 breaths in cach minute and with each inhalation and exhalation moving about 500 mL of air into and out of the lungs. The volume of one breath is called the tidal volume (VT).
2. Minute Ventilation (MV)
We are doing 12 breaths in each minute so the minute ventilation (MV) is the the total volume of air inhaled and exhaled in each minute.
Minute Ventilation (MV)
Tidal volume (VT) x 12
=500 mL/breath x 12 breaths/min=6 litres/min
In a typical adult, about 70% of the tidal volume (350 mL) actually reaches the respiratory zone of the respiratory system namely the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli and participates in external respiration.
The other 30% (150 mL) remains in the conducting airways of the nose,pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles known as dead space because these part does not undergo respiratory exchange of gases
Not all of the minute ventilation can be used in gas exchange because some of it remains in the anatomic dead space.
3. Alveolar Votiation Rate
The sheeler ventilation rate is the volume of air per minute that actually reaches the respiratory zone.
in the example just given, alveolar ventilation rate would be 150 mL/besath x 12 terrath/min=4200 mL/min
4. Ispiratory Reserve Volume
When we do very deep breath, we can inhale more than 500 mL of air. This addional inhaled ar, called the inspiratory reserve volume which is about 3100mL in an average adult male and 1900 ml in an average adult female.
5. Expiratory Reserve Volume or Force Expiratory Volume
If inhalation follows forced exhalation we can more air in addition to the 500 mL of tidal volume which is 1200 mL in males and 700 mL in females is called the expiratory reserve volume or force expiratory volume.
ELECTROCARDIOGRAPHY: ECG
Electrocardiography (ECG or EKG from the German Elektrokardiogramm) is a transthoracic interpretation of the electrical activity of the heart over time captured
and externally recorded by skin electrodes. • It is a noninvasive recording produced by an electrocardiographic device. .
The ECG works mostly by detecting and amplifying the tiny electrical changes on the skin that are caused when the heart muscle “depolarizes” during each heart beat.
At rest, each heart muscle cell has a charge across its outer wall, or cell membrane. Reducing this charge towards zero is called de-polarization, which activates the mechanisms in the cell that cause it to contract
During each heartbeat a healthy heart will have an orderly progression of a wave of depolarization that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through intrinsic conduction pathways” and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.
Usually more than 2 electrodes are used and they can be combined into a number of pairs. (For example: Left arm (LA), right arm (RA) and left leg (LL) electrodes form the pairs: LA+RA, LA LL, RA+LL) The output from each pair is known as a lead. Each lead is said to look at the heart from a different angle.
Different types of ECGs can be referred to by the number of leads that are recorded, for example 3-lcad, 5-lead or 12-Icad ECGs (sometimes simply “a 12-lead”)
A 12-lead ECG is one in which 12 different electrical signals are recorded at approximately the same time and will often be used as a one-off recording of an ECG, typically printed out as a paper copy. 3- and 5-lead ECGs tend to be monitored continuously and viewed only on the screen of an appropriate monitoring device, for example during an operation or whilst being transported in an ambulance.
There may, or may not be any permanent record of a 3- or 5-lead ECG depending on the equipment used.
functions and structure of respiratory system
Allows you to talk and to smell.
Warms air to match your body temperature and moisturizes it to the humidity level your body needs.
Delivers oxygen to the cells in your body.
Removes waste gases, including carbon dioxide, from the body when you exhale.
Protects your airways from harmful substances and irritants.
Anatomy
Mouth and nose: Openings that pull air from outside your body into your respiratory system.
Sinuses: Hollow areas between the bones in your head that help regulate the temperature and humidity of the air you inhale.
Pharynx (throat): Tube that delivers air from your mouth and nose to the trachea (windpipe).
Trachea: Passage connecting your throat and lungs.
Bronchial tubes: Tubes at the bottom of your windpipe that connect into each lung.
Lungs: Two organs that remove oxygen from the air and pass it into vour blood
Mechanism of Breathing
The air that we breathe in and out of the lungs varies in its pressure. So basically when there is a fall in air pressure the alveolar spaces fall and the air enters the lungs (inspiration) and as the pressure of the alveoli within exceeds the atmospheric pressure, the air is blown from the lungs (expiration). The flow rate of air is in proportion to the magnitude of the pressure difference.
The breathing mechanism involves two processes:
• Inspiration
• Expiration
Inspiration
In the process of inspiration, there would be a contraction of muscles attached to the ribs on the outer side which pulls out the ribs and results in the expansion of the chest cavity.
Later, the diaphragm, contracts, moves downwards and expands the chest cavity resulting in the contraction of the abdominal muscles.
The expansion of the chest cavity produces a partial vacuum which sucks air into the lungs and fills the expanded alveoli.
Structure the heart
The heart wall is composed of three layers, Including the outer epicardium (thin layer), middle myocardium (thick layer), and innermost endocardium (thin layer). The myocardium is made up of cardiac muscle fibers and is responsible for the contraction and relaxation that results in the pumping of the heart.
The two atria have a thinner myocardium layer than the ventricles, as the force required for atrial contractions is much less than that needed for ventricular contractions. The walls of the right ventricle are also thinner, as this ventricle only pumps blood a short distance to the lungs. Comparatively, the left ventricle, which has much thicker walls, must generate enough force to pump oxygenated blood throughout the rest of the body.
The myocardium requires a constant supply of oxygen and nutrients to maintain the contractions and relaxations that keep the heart pumping. This blood supply is maintained through a set of coronary arteries and veins in the myocardium.
The right and left coronary arteries, which branch off the first section of the aorta known as the ascending aorta between the left ventricle and aortic arch, supply blood to a network of capillaries in the myocardium. Deoxygenated blood from the myocardium is carried through a set of cardiac veins to the right atrium that is subsequently drained through the coronary sinus.
Function:
1. The heart’s primary function is to pump blood throughout the body.
2. It supplies oxygen and nutrients to the tissues and removes carbon dioxide and waste from the blood.
3. It also helps to maintain adequate blood pressure throughout the body.
4. Heart pumps the blood throughout the body, hence playing an important role in maintaining body temperature.
