#OxytocinHormone

#Biology

#EndocrineSystem

Introduction

• Oxytocin is a pituitary neuropeptide that have been shown to affect social processes in mammals.

• Neuropeptides are chemical messengers that are produced by neurons and are made up of short chains of amino acids.

• 3 Major Functions of Oxytocin :

  • Labor and childbirth - Oxytocin stimulates uterine contractions to induce labor and birth. It's sometimes given to women in labor to speed up the process.

  • Lactation - Oxytocin stimulates breast tissue contractions to help with milk production after birth.

  • Social interactions - Oxytocin is a chemical messenger in the brain that influences many human behaviors and social interactions, including:

    • Sexual arousal

    • Recognition

    • Trust

    • Romantic attachment

    • Parent-infant bonding 

• Your pituitary gland, found at the base of your brain, stores oxytocin and then releases it into your bloodstream when triggered by the electrical activity of neurons in the hypothalamus.

Labour and Childbirth

• 3 Major Functions of Oxytocin in Labour and Childbirth :

  • Stimulating uterine contractions.

  • Reducing stress.

  • Preventing heavy bleeding.

• When the fetus's body pushes against the cervix, nerve impulses travel to the brain and stimulate the pituitary gland to release oxytocin. Oxytocin activates calcium channels in the smooth muscle cells, which releases calcium from the sarcoplasmic reticulum.

• Oxytocin receptors are G protein-coupled receptors that bind to Gαq/11 and Gαi3 proteins. This activates phospholipase C, which produces inositol trisphosphate (IP3). IP3 then stimulates the release of calcium from intracellular stores.

• The release of calcium initiates the muscle contraction cycle.

• An action potential travels into the T-tubule, which activates voltage-sensitive dihydropyridine receptors (DHPRs).

• DHPRs trigger the opening of ryanodine receptors (RyR), which release calcium from the sarcoplasmic reticulum (SR).

• Calcium binds to troponin, which moves tropomyosin off the myosin binding sites on actin.

• Myosin motors crawl along actin, forming cross-bridges and shortening the muscle fiber.

• The muscle contracts as the sarcomere shortens.

• When the action potential ends, calcium pumps remove calcium from the cytosol and back into the SR. Tropomyosin moves back into position, blocking the myosin binding site on actin, and the muscle relaxes.

• Oxytocin can reduce the secretion of CRF and glucocorticoids, which are involved in the stress response.

• Oxytocin reduces CRF and glucocorticoids by inhibiting the secretion of adrenocorticotropic hormone (ACTH), which decreases the production and release of cortisol.

• Oxytocin prevents excessive bleeding after childbirth by stimulating uterine contractions, which constrict spiral arteries and reduce blood flow through the uterus.

Lactation

• When a baby suckles, the nipple is stimulated, which triggers the release of oxytocin. Oxytocin causes the myoepithelial cells in the breast to contract, forcing milk from the alveoli through the ducts and out of the nipple.

• Oxytocin causes myoepithelial cells to contract by binding to a G protein-coupled receptor (OTR). This contraction is a key part of the milk ejection reflex, which occurs when a baby suckles.

Social Interactions

• Men - Oxytocin activates neurons in the spinal ejaculation generator (SEG) and influences male sexual function. Oxytocin levels increase during arousal and peak at orgasm. One study found that a nasal spray of oxytocin could help men with delayed orgasm or failure to orgasm.

• Women - Oxytocin plays a role in orgasm. One study found that women had significantly higher oxytocin levels less than a minute after orgasm. Oxytocin may also help sperm reach the destination by increasing uterine motility.

• Oxytocin can improve voice-identity recognition. One study found that oxytocin increased responses to voice identity recognition in the right posterior superior temporal sulcus/gyrus (pSTS/G), a region of the brain involved in analyzing voice-identity information.

• When you hug or kiss a loved one, your pituitary gland releases oxytocin. This is especially important for pair bonding, like in romantic relationships, as it elevates your mood and makes you feel more "attached" to your romantic partner.