Human Physiology: A Comprehensive Guide to the Body’s Functions

Posted on May 24, 2024 in Biology

Renin-Angiotensin-Aldosterone System (RAAS)

The renin-angiotensin-aldosterone system (RAAS) is a 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.

Cardiac Cycles

A cardiac cycle includes all the events associated within one heartbeat. The normal heart beats in healthy adults is 75 beats/min and a cardiac cycle lasts for 0.8 sec. In the cardiac 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 cardiac cycle is described by the following phases:

1. Atrial systole – In this phase, atrial contraction begins, which lasts about 0.1 sec. At the same time, the ventricles are relaxed. So, the right and left AV valves are open, and the atria send blood into the relaxed ventricles.
2. Ventricular systole – In this phase, the ventricles begin contraction, which lasts for 0.3 sec. Pressure in the ventricles rises due to contraction and shuts the AV valves, which is heard by the”Lub” sound. For about 0.05 sec, all four valves are closed, which is known as isovolumetric contraction. Ventricular contraction pushes blood out of the ventricles and opens both semilunar valves and ejects 70 ml of blood into the aorta and the same amount of blood into the pulmonary trunk.

Creatinine Clearance Test

The creatinine clearance test is a test that checks 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.

Composition of Lymph

The lymphatic system comprises:

• Lymph plasma
• Lymph corpuscles
• Lymphoid organs

Lymph plasma – Lymph is an 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 structures 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 adults doing 12 breaths in each 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).

We are doing 12 breaths in each minute, so the minute ventilation (MV) is 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 liters/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 parts do 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.

The alveolar ventilation rate is the volume of air per minute that actually reaches the respiratory zone.

In the example just given, the alveolar ventilation rate would be 150 mL/breath x 12 breaths/min = 4200 mL/min

When we do very deep breaths, we can inhale more than 500 mL of air. This additional inhaled air, called the inspiratory reserve volume, is about 3100 mL in an average adult male and 1900 mL in an average adult female.

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”depolarize” during each heartbeat.

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.

Types of Nephron

There are two types of nephron:

• Cortical nephron-These are the nephrons present within the cortex. These are short and comprise about 80% of the total nephrons. Juxtamedullary nephron-These have long loops of Henle and extend into the medulla. These are about 20%. Functions of Nephron

PHYSIOLOGY OF MUSCLE CONTRACTION

Contraction and Relaxation of Skeletal Muscle Fibers: The contraction and relaxation of skeletal muscle fibers occurs in following steps. Muscle contraction occurs because cross-bridges attach to and “walk along the thin on at both ends of a sarcomere, progressively pulling the thin filaments toward the of a sarcomere. As the thin filaments slide inward, the Z discs come closer together, sarcomere shortens. Contraction cycle: The contraction cycle is the repeating sequence of events that adding of the filaments (a) Myosin ATPase hydrolyzes ATP and becomes energized, (b)The myosin head attaches to actin, forming a crossbridge, (c)The crossbridge generates force as it rotates toward the center of the sarcomere stroke (d)Binding of ATP to the myosin, head detaches it from actin. The myosin head again hydrolyzes the ATP, return to its original position, and binds to a new site on actin as the continues  An increase in Ca2+ concentration in the cytosol starts filament sliding, a decrease off the sliding process The muscle action potential propagating into the T tubule system causes opening of release channels in the SR membrane. Calcium ions diffuse from the SR into the data combine with troponin. This binding causes tropomyosin to move away from the binding sites.

Skin

The skin is the largest organ in the human body and plays a vital role in protecting the body from external harm. It also serves as a sensory receptor for touch, pressure, temperature, and pain sensations. (Parts)Anatomy of the skin:  Epidermis – the outermost layer of the skin that provides a protective barrier  Dermis – the underlying layer of the skin that contains blood vessels, nerves, hair follicles, and sweat glands  Subcutaneous layer (hypodermis) – the deepest layer of the skin that contains fat and connective tissue. Function- The epidermis provides a barrier to protect against external damage and prevent water loss.  The dermis contains sensory receptors that detect touch, pressure, temperature, and pain.  The subcutaneous layer provides insulation and helps regulate body temperature.  The skin also contains sweat glands that help regulate body temperature through sweating and oil glands that keep the skin moisturized. .

Hormones of pituitary gland

Growth/somatotropic hormone (GH/STH)— GH is responsible for the general growth of the body. Over-secretion of GH stimulates abnormal growth of the body leading to gigantism and low secretion of GH results in stunted growth resulting in pituitary dwarfism.  Thyroid stimulating hormone (TSH)— TSH stimulates the synthesis and secretion of thyroid hormones from the thyroid gland. Adrenocorticotropic hormone (ACTH)— ACTH stimulates the synthesis and secretion of steroid hormones called glucocorticoids from the adrenal cortex  Prolactin (PRL)— Prolactin regulates the growth of the mammary glands and formation of milk in them.  Follicle stimulating hormone (FSH) and luteinizing hormone (LH)— LH and FSH stimulate gonadal activity and hence are called gonadotrophins. In males, LH stimulates the synthesis and secretion of hormones called androgens from testis.

The axial skeleton. Axial skeleton forms the longitudinal axis of the body and protects the brain, spinal cord, and the organ in the thorax. It provides support to the head, neck, and trunk. Axial skeleton are composed by the 80 bones segregated into three major regions.A. Skull. B. Vertebral column. C. Thoracic cage. Skull bone. Most of skull bone are flatted and firmly united by interlocking joints called sutures but mandible bone which is connected to the rest of the skull freely movable bones. A. Skull. B. Vertebral column. C. Thoracic cage. Skull bone. Most of skull bone are flatted and firmly united by interlocking joints called sutures but mandible bone which is connected to the rest of the skull freely movable bones.

Vertebral column- Vertebral column also called as spine or spinal column, it consists of 26 irregular serially arranged unit called as vertebrae and dorsally placed. In the fetus and infants, the vertebral column consists of 33 separate bones or vertebrae. In adult age , nine of these eventually fuse to form two composites bones, the sacrum and coccyx the remaining 25 bones persists at individual vertebrae separates by intervertebral discs.  

Physiology of menstruation

Menstrual cycle is defined as the natural cyclic changes occurs in the female life during the reproductive period. Menstrual cycle stops/ceases in old age called menopause (at the age 45 to 50 years it also varies individual to individual). Menstrual cycle is usually 28 days but it varies between 20 to 40 days under the physiological conditions. Four types of physiological changes happen during the menstrual cycle—  Ovarian changes.  Uterine changes.  Vaginal changes.  Changes in cervix. 1. Ovarian changes— It occurs into two phasesA. Follicular phase— it is also known as maturation phase. It extends from the 5th day of the cycle until the time of ovulation. In this phase gamete cell going to development and transformation into ovarian follicle/glandular structure. Follicle development further divide into four stages. I. Primordial follicle— At the time of puberty, both ovaries contain about 400,000 primordial follicles, which is incompletely surrounded by the granulosa cells. At the onset of puberty, under the influence of FSH and LH the primordial follicles starts growing through various stages. II. Primary follicle— Primordial follicle becomes the primary follicle, when ovum is completely surrounded by the granulosa cells. During this stage both follicle and ovum increase their size. III. Vesicular follicle— Under the influence of FSH, about 6 to 12 primary follicles start growing and develops into vesicular follicles. In this stage a follicular cavity or antrum is formed in these liquor folliculi serous fluid is present.  Ovum is pushed to one side and it is surrounded by granulosa cells, which forms the germ hill or cumulus oophorus. Further these cells become columnar and form corona radiata.  A narrow cleft appears between ovum and zona pellucida called perivitelline space.  Follicular sheath/theca folliculi/capsule is formed and it divided into two layers – theca interna and theca externa.Theca interna is the inner vascular layer with loose connective tissue and secrete the female sex hormones (mainly estrogen and less amount of progesterone). IV. Matured follicle or Graafian follicle (A Dutch physician and anatomist, Regnier De Graaf)— After about 7th day of menstrual cycle, one of the vesicular follicles outgrowths and develops into Graafian follicle and follicles degenerate by means of apoptosis. In this stage ovum attain maximum size and zona pellucida, corona radiata, theca interna becomes thicker and more prominent.  

Spermatogenesis.

Spermatogenesis is the process through which spermatogenic/germ cell undergo the development and transformation and form the spermatozoa or sperms cell in the testis. It takes 74 days for the formation of sperm from a primitive germ cell. Spermatogenesis occurs in four stages1. Stage of proliferation. 2. Stage of growth. 3. Stage of maturation. 4. Stage of transformation. 1. Stage of proliferation— Each spermatogonium contains diploid number (23 pairs) of chromosomes, In which 22 pairs of autosomal chromosomes and one pair of sex chromosomes. Sex chromosomes are one X chromosome and one Y chromosome. In this stage spermatogonia divides by mitosis and increase their number without any change in the chromosomal number which is called as primary spermatocyte. 2. Stage of growth— In this stage, the primary spermatocyte grows into a large cell. Apart from growth, there is no change in spermatocyte during this stage. 3. Stage of maturation— after completion of full growth cell undergoes meiotic or maturation division. It occurs into two phases.  First phase—During this phase primary spermatocyte divides into two secondary spermatocytes through meiotic division in that each secondary spermatocyte receives only the haploid or half the number of chromosomes. 23 chromosomes include 22 autosomes and a X or a Y chromosome.  Second phase— During this phase, each secondary spermatocyte undergoes second meiotic division, resulting in two smaller cells called spermatids. Each spermatid has haploid number of chromosomes. 4. Stage of transformation— In this stage no further division occurs, and spermatids get transformed into mature spermatozoa this transformation process is known as spermiogenesis. Finally mature spermatozoa released from Sertoli cell into the lumen of seminiferous tubule and this process is known as spermination.