Sexual Dimorphism & Endocrine System

Sexual Dimorphism in the Neural System

• The sexually dimorphic nucleus of the preoptic area (SDN-POA) is larger in male rats than in females

Endocrine Systems

• Major endocrine structures include the hypothalamus, pineal gland, pituitary gland (anterior and posterior), thyroid, adrenal glands (cortex and medulla), pancreas, gut, and gonads (testes/ovaries)
• The hypothalamus controls hormone secretions
• The pineal gland regulates reproductive maturation and body rhythms
• The anterior pituitary is responsible for hormone secretion by the thyroid, adrenal cortex, and gonads, and growth
• The posterior pituitary regulates water balance and salt balance
• The thyroid controls growth and development as well as metabolic rate
• The adrenal cortex regulates salt and carbohydrate metabolism and inflammatory reactions
• The adrenal medulla controls emotional arousal (epinephrine)
• The pancreas handles sugar metabolism
• The gut controls digestion and appetite
• The gonads control body development and the maintenance of reproductive organs in adults

Physiological Signaling Systems

• Neural signaling involves direct electrical connections with short and long range and acute signaling
• Endocrine signaling includes systemic release and circulation of signaling molecules with short and long range and is long lasting
• Pheromone signaling involves the external release of signaling molecules to invoke a physiological response from members of the same species and is long lasting
• Allomone signaling involves the external release of signaling molecules to invoke a physiological response from different species and is long lasting

Hormone Structure

• Hormones are categorized into three types: peptide, amine, and steroid
• Peptide hormones are composed of short strings of amino acids and are typical of neuropeptides
• Amine hormones are modified versions of single amino acids
• Steroid hormones are derived from cholesterol and have complex modified structures

Hormone Mechanism of Action

• Peptide and amine based hormones are receptor-based and require the expression of specific membrane-bound receptors to bind
• Steroid hormones are diffusible and pass freely through lipid membranes and bind intracellular receptors

Hypothalamus and Posterior Pituitary

• The production and release of hormones, including oxytocin and vasopressin, require coordination between the hypothalamus and pituitary gland
• Specialized neuroendocrine cells in the hypothalamus generate hormones
• There is a direct connection between the hypothalamus and pituitary through electrical and transport mechanisms
• Stimulation occurs via projecting neurons to invoke the release of hormones

Feedback Loops Regulate Endocrine Release

• Negative feedback generally occurs in response to extended biological action
• Positive feedback loops exist but are relatively rare

Thermoregulation

• Thermoregulation is a regulatory process in the body
• Actively regulates both acute temperature and temperature shift
• Involves neural processing
• Involves both complex physiological response and behaviors

Regulation of Osmolarity

• Highly redundant system involving receptors in multiple tissues
• Osmotic thirst is purely neural, osmoregulatory receptors detect high extracellular sodium
• Hypovolemic thirst: loss of volume in blood and is sensed and compensated for by the intake of fluid volume

Regulation of Metabolism

• Heavily regulated using multiple hormone based regulatory mechanism
• High level of neural input helps to modulate sensing and response