Insulin

In this article, we will discuss Insulin. So, let’s get started.

Insulin

Insulin is a peptide hormone, which is important for metabolism and utilization of energy from the ingested nutrients, especially glucose. There are 51 amino acids in an insulin molecule. It has a molecular weight of 5808 Da. Insulin is produced in the islets of Langerhans in the pancreas. The name insulin comes from the Latin word “insula” for “island” from the cells that produce the hormone in the pancreas.

Synthesis

Beta cells of islets of Langerhans in the pancreas

Enters portal circulation

Liver (prime target organ)

(50% of insulin is extracted and degraded in the liver)

C-peptide is partially extracted by the liver

Kidney (Residue and C-peptide are broken down here)

Physiological effects

  • Insulin increases cellular intake of glucose in muscles and adipose tissues.
  • Insulin increases DNA replication and protein synthesis via control of amino acid uptake.
  • It modifies the activity of numerous enzymes.
  • Insulin increases fat synthesis.
  • Insulin increases the esterification of fatty acids.
  • It induces glycogen synthesis, decreases gluconeogenesis and glycogenolysis.
  • It decreases proteolysis, lipolysis, and autophagy.
  • Increases amino acid and potassium uptake.
  • Increases secretion of HCl by parietal cells in the stomach.
  • Insulin forces the arterial wall muscle to relax thereby increasing blood flow (especially in micro arteries).
  • Insulin decreases renal sodium excretion.
  • Insulin has stimulatory effects on gonadotrophin-releasing hormone by the hypothalamus, thus favoring fertility.
  • Insulin also influences body functions such as vascular compliance, homeostasis, and cognition

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Reflex Pathway of Vomiting

In this article, we will discuss the Reflex Pathway of Vomiting. So, let’s get started.

Pathway

Central control: Vomiting is controlled by two centers located in the medulla, i.e. vomiting center in the lateral reticular formation and chemoreceptor trigger zone in the floor of the fourth ventricle.

Afferent pathway: The vomiting center receives afferent impulses from the GI tract, from the brainstem and cortical centers especially labyrinthine apparatus and from the chemoreceptor trigger zone. The chemoreceptor trigger zone by itself is incapable of mediating the act of vomiting, the activation of this zone results in efferent impulses to the medullary vomiting center, which in turn initiates the vomiting.

Efferent pathway: The important efferent pathways in vomiting are phrenic nerves (to the diaphragm), spinal nerves (to the intercoastal and abdominal muscles) and visceral efferent fibers in the vagus nerve (to the larynx, pharynx, esophagus, and stomach).