NEET MDS Lessons
Physiology
Neurons :
Types of neurons based on structure:
a multipolar neuron because it has many poles or processes, the dendrites and the axon. Multipolar neurons are found as motor neurons and interneurons. There are also bipolar neurons with two processes, a dendrite and an axon, and unipolar neurons, which have only one process, classified as an axon.. Unipolar neurons are found as most of the body's sensory neurons. Their dendrites are the exposed branches connected to receptors, the axon carries the action potential in to the central nervous system.
Types of neurons based on function:
- motor neurons - these carry a message to a muscle, gland, or other effector. They are said to be efferent, i.e. they carry the message away from the central nervous system.
- sensory neurons - these carry a message in to the CNS. They are afferent, i.e. going toward the brain or spinal cord.
- interneuron (ie. association neuron, connecting neuron) - these neurons connect one neuron with another. For example in many reflexes interneurons connect the sensory neurons with the motor neurons.
Regulation of Blood Pressure by Hormones
The Kidney
One of the functions of the kidney is to monitor blood pressure and take corrective action if it should drop. The kidney does this by secreting the proteolytic enzyme renin.
- Renin acts on angiotensinogen, a plasma peptide, splitting off a fragment containing 10 amino acids called angiotensin I.
- angiotensin I is cleaved by a peptidase secreted by blood vessels called angiotensin converting enzyme (ACE) — producing angiotensin II, which contains 8 amino acids.
- angiotensin II
- constricts the walls of arterioles closing down capillary beds;
- stimulates the proximal tubules in the kidney to reabsorb sodium ions;
- stimulates the adrenal cortex to release aldosterone. Aldosterone causes the kidneys to reclaim still more sodium and thus water.
- increases the strength of the heartbeat;
- stimulates the pituitary to release the antidiuretic hormone (ADH, also known as arginine vasopressin).
All of these actions, which are mediated by its binding to G-protein-coupled receptors on the target cells, lead to an increase in blood pressure.
The hypothalamus is a region of the brain. It secretes a number of hormones.
- Thyrotropin-releasing hormone (TRH)
- Gonadotropin-releasing hormone (GnRH)
- Growth hormone-releasing hormone (GHRH)
- Corticotropin-releasing hormone (CRH)
- Somatostatin
- Dopamine
All of these are released into the blood, travel immediately to the anterior lobe of the pituitary, where they exert their effects.
Two other hypothalamic hormones:
- Antidiuretic hormone (ADH) and
- Oxytocin
travel in neurons to the posterior lobe of the pituitary where they are released into the circulation.
The pituitary gland is pea-sized structure located at the base of the brain. In humans, it consists of two lobes:
- the Anterior Lobe and
- the Posterior Lobe
The Anterior Lobe
The anterior lobe contains six types of secretory cells All of them secrete their hormone in response to hormones reaching them from the hypothalamus of the brain.
Thyroid Stimulating Hormone (TSH)
TSH (also known as thyrotropin) is a glycoprotein The secretion of TSH is
- stimulated by the arrival of thyrotropin releasing hormone (TRH) from the hypothalamus.
- inhibited by the arrival of somatostatin from the hypothalamus.
TSH stimulates the thyroid gland to secrete its hormone thyroxine (T4).
Some develop antibodies against their own TSH receptors making more T4 causing hyperthyroidism. The condition is called thyrotoxicosis or Graves' disease.
Hormone deficiencies
A deficiency of TSH causes hypothyroidism: inadequate levels of T4 (and thus of T3 )..
Follicle-Stimulating Hormone (FSH)
FSH is a heterodimeric glycoprotein Synthesis and release of FSH is triggered by the arrival from the hypothalamus of gonadotropin-releasing hormone (GnRH).
FSH in females :In sexually-mature females, FSH (assisted by LH) acts on the follicle to stimulate it to release estrogens.
FSH in males :In mature males, FSH acts on spermatogonia stimulating (with the aid of testosterone) the production of sperm.
Luteinizing Hormone (LH)
LH is synthesized within the same pituitary cells as FSH and under the same stimulus (GnRH). It is also a heterodimeric glycoprotein
LH in females
In sexually-mature females, LH
- stimulates the follicle to secrete estrogen in the first half of the menstrual cycle
- a surge of LH triggers the completion of meiosis I of the egg and its release (ovulation) in the middle of the cycle
- stimulates the now-empty follicle to develop into the corpus luteum, which secretes progesterone during the latter half of the menstrual cycle.
LH in males
LH acts on the interstitial cells (also known as Leydig cells) of the testes stimulating them to synthesize and secrete the male sex hormone, testosterone.
LH in males is also known as interstitial cell stimulating hormone (ICSH).
Prolactin (PRL)
Prolactin is a protein of 198 amino acids. During pregnancy it helps in the preparation of the breasts for future milk production. After birth, prolactin promotes the synthesis of milk.
Prolactin secretion is
- stimulated by TRH
- repressed by estrogens and dopamine.
Growth Hormone (GH)
- Human growth hormone (also called somatotropin) is a protein
- The GH-secreting cells are stimulated to synthesize and release GH by the intermittent arrival of growth hormone releasing hormone (GHRH) from the hypothalamus. GH promotes body growth
In Child
- hyposecretion of GH produces dwarfism
- hypersecretion leads to gigantism
In adults, a hypersecretion of GH leads to acromegaly.
ACTH — the adrenocorticotropic hormone
ACTH acts on the cells of the adrenal cortex, stimulating them to produce
- glucocorticoids, like cortisol
- mineralocorticoids, like aldosterone
- androgens (male sex hormones, like testosterone
Hypersecretion of ACTH cause of Cushing's disease.
Normal Chemical Composition of Urine
Urine is an aqueous solution of greater than 95% water, with a minimum of these remaining constituents, in order of decreasing concentration:
Urea 9.3 g/L.
Chloride 1.87 g/L.
Sodium 1.17 g/L.
Potassium 0.750 g/L.
Creatinine 0.670 g/L .
Other dissolved ions, inorganic and organic compounds (proteins, hormones, metabolites).
Urine is sterile until it reaches the urethra, where epithelial cells lining the urethra are colonized by facultatively anaerobic gram-negative rods and cocci. Urea is essentially a processed form of ammonia that is non-toxic to mammals, unlike ammonia, which can be highly toxic. It is processed from ammonia and carbon dioxide in the liver.
Asthma = Reversible Bronchioconstruction 4%-5% of population
Extrinsic / Atopic = Allergic, inherited (familia), chromosome 11
IgE, Chemical Mediators of inflammation
a. Intrinsic = Negative for Allergy, Normal IgE, Negative Allergic Tests
Nucleotide Imbalance cAMP/cGMP: cAMP = Inhibits mediator release, cGMP = Facilitates mediator release
b. Intolerance to Asprin (Triad Asthma)
c. Nasal Polyps & Asthma
d. Treatment cause, Symptoms in Acute Asthma
1. Bronchial dilators
2. steroids edema from Inflamation
3. Bronchiohygene to prevent Secondary Infection, (Remove Excess Mucus)
4. Education
Functions of the nervous system:
1) Integration of body processes
2) Control of voluntary effectors (skeletal muscles), and mediation of voluntary reflexes.
3) Control of involuntary effectors ( smooth muscle, cardiac muscle, glands) and mediation of autonomic reflexes (heart rate, blood pressure, glandular secretion, etc.)
4) Response to stimuli
5) Responsible for conscious thought and perception, emotions, personality, the mind.