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NEET MDS Synopsis - Lecture Notes
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📖 Physiology

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The large intestine (colon)
Physiology

The large intestine (colon)

The large intestine receives the liquid residue after digestion and absorption are complete. This residue consists mostly of water as well as materials (e.g. cellulose) that were not digested. It nourishes a large population of bacteria (the contents of the small intestine are normally sterile). Most of these bacteria (of which one common species is E. coli) are harmless. And some are actually helpful, for example, by synthesizing vitamin K. Bacteria flourish to such an extent that as much as 50% of the dry weight of the feces may consist of bacterial cells. Reabsorption of water is the chief function of the large intestine. The large amounts of water secreted into the stomach and small intestine by the various digestive glands must be reclaimed to avoid dehydration.

Neural Substrates of Breathing
Physiology

Neural Substrates of Breathing

A.    Medulla Respiratory Centers

Inspiratory Center (Dorsal Resp Group - rhythmic breathing) → phrenic nerve→ intercostal nerves→ diaphragm + external intercostals

Expiratory Center (Ventral Resp Group - forced expiration) → phrenic nerve → intercostal nerves → internal intercostals + abdominals (expiration)

1.    eupnea - normal resting breath rate (12/minute)
2.    drug overdose - causes suppression of Inspiratory Center

B.    Pons Respiratory Centers

1.    pneumotaxic center - slightly inhibits medulla, causes shorter, shallower, quicker breaths
2.    apneustic center - stimulates the medulla, causes longer, deeper, slower breaths

C.    Control of Breathing Rate & Depth

1.    breathing rate - stimulation/inhibition of medulla
2.    breathing depth - activation of inspiration muscles
3.    Hering-Breuer Reflex - stretch of visceral pleura that lungs have expanded (vagal nerve)

D.    Hypothalamic Control - emotion + pain to the medulla

E.    Cortex Controls (Voluntary Breathing) - can override medulla as during singing and talking

Hormones of the Pituitary

Physiology

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.

RESPIRATORY DISORDERS - .Hyperventilation
Physiology

Hyperventilation

  1. Treatments :Rebreath air, hold breath (Increase CO2)
    Give oxygen for Hypoxemia