[Endocrinology] The pineal gland

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This structure is a component of the brain.
The pineal gland regulates sleep and metabolism.

 

Input

Inhibited by

• Sensation of light by retinal cells, via the suprachiasmatic nucleus (SCN)

 

Output

• Melatonin: modulates CNS activity to promote sleep
• Unknown signalling mechanism: modulates pituitary gland activity, increases the concentration of FSH and LH within the pituitary gland

 

Function

The suprachiasmatic nucleus (SCN) is a structure in the brain, which regulates the circadian rhythm of the body. The SCN receives information from the retinae about the levels of available light and becomes oriented to the time of day. It modulates the activity of the pineal gland to promote sleep and modulate metabolism.

Hormones

• Melatonin

 

Pathology

• Circadian rhythm disturbances 
• Evening use of artificial light sources is a risk factor for sleep disturbances, including insomnia. White light sources which produce a high proportion of blue light (high frequency visible light waves) are particularly potent at inhibiting melatonin secretion.
• Metabolic disturbances  
• Excessive or insufficient levels of sleep are a risk factor for developing type 2 diabetes.

Basal ganglia

This structure is a component of the brain. 

 

Physiology

In the human brain, there is a map of every skeletal muscle, called the motor cortex. It is a collection of upper motor neurons, each of which initiates a signal down the spine to the muscle it corresponds to. The brain is constantly trying to anticipate and prepare for actions, so signals are constantly being sent to these muscles. If there is no inhibition of these signals, purposeless movements would constantly occur. The basal ganglia have evolved to provide a locking mechanism here.

The basal ganglia are a system of neural circuitry which provides logical processing of these signals before they can continue to reach the body. They consist of the striatum, globus pallidus, ventral pallidum, substantia nigra, and subthalamic nucleus. These each behave differently and they interact like components of an electronic microchip. Most of the components have an overall inhibitory effect on outgoing signals. They block unnecessary motor neuron signals.

When a healthy person decides to contract their bicep muscle to flex their arm, the brain sends signals to the basal ganglia, which tell neurons there to release a neurotransmitter called dopamine. The dopamine bind to other neurons and switches the activity "mode" of the cells. This has an effect of removing inhibition on the outgoing signals. The basal ganglia do not only modulate motor signalling. They have connections to the oculo-motor, associative, limbic and orbitofrontal circuits. The motor function is the easiest to assess and the most vital for survival, so it is the most well-researched.

Basal ganglia diseases

The hypothalamus and pituitary

Organ system: Endocrine system

Medical specialty: Endocrinology

This structure is a component of the brain. 

 

Anatomy

The hypothalamus is a structure of the brain. It sits below the thalamus (this is what hypo-thalamus means), but above the pituitary. 

The pituitary (also called the hypophysis) sits in the "sella turcica" in the floor of the sphenoid bone (one of the bones which comprise the skull).

 

Embryology

In early development, the prosencephalon (forebrain) divides into the diencephalon and telencephalon.

The telencephalon eventually becomes the cerebral cortex and the basal ganglia.
The diencephalon becomes the third ventricle, the thalamus, the hypothalamus and the posterior pituitary.

 

Physiology

The anterior pituitary is a gland which stores and releases important hormones into the circulatory system. The hypothalamus communicates with it through a rich system of blood vessels. This system is called the hypothalamic-hypophyseal portal system. 

The posterior pituitary is a collection of axonal projections (the transmitting fibres of neurons) from the hypothalamus. Hormones are secreted from these projections, into a network of blood vessels. 

The hypothalamus and the pituitary work as the bridge between the central nervous system and the endocrine system. By releasing hormones into the circulatory system, the brain can coordinate widespread cellular signalling throughout the whole body. These endocrine signals are slow to cause action, but the effects can last for a long time.
The spinal cord on the other hand, is useful for rapid signal transmission from the brain to the body.

 

Primary signalling targets

• Somatotropes
• Output: Human growth hormone (hGH)
• Effect: Stimulates growth in body cells
• Lactotropes
  • Output: Prolactin (PRL)
  • Effect: Stimulates milk production in the mammary glands
• Gonadotropes
• Output: Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)
• Effect: Stimulates hormone release from the gonads
• Corticotropes 
• Output: Adrenocorticotropic hormone (ACTH)
• Effect: Stimulates hormone release from the adrenal glands
• Thryotropes
• Output: Thyroid stimulating hormone (TSH)
• Effect: Stimulates hormone release from the thyroid gland

• Posterior pituitary 
• Output: Oxytocin
• Effect: Stimulates milk ejection from the mammary glands 
• Effect: Stimulates muscular contractions of the uterus
• Posterior pituitary
• Output: Anti-diuretic hormone (Vasopressin)
• Effect: Promotes water retention in the kidneys

 

Hormones

• Human growth hormone (hGH)
• Prolactin (PRL)
• Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)
• Adrenocorticotropic hormone (ACTH)
• Thyroid stimulating hormone (TSH)
• Oxytocin
• Anti-diuretic hormone (Vasopressin)

 

Pathology

• Hyperpituitarism (excessive pituitary activity) 
• Gigantism or acromegaly  
• Unexpected lactation
• Hypercortisolism (Cushing's disease)
• Hypopituitarism (insufficient pituitary activity)
• Oligo- or amenorrhoea  
• Infertility
• Pituitary dwarfism
• Hypocortisolism (Addison's disease) 
• Pituitary adenoma

The brain

The brain and spinal cord together form the central nervous system (CNS). 

 

Components  

• Pineal gland 
• Hypothalamus and pituitary 
• Basal ganglia 

 

Microscopic structure

Cognition and memory rely on neurons (nerve cells) and the synapses (connections) between them. The genetic (the combination of genes in the DNA) and epigenetic (the regulation of which genes are active or inactive) mechanisms in each neurone regulate its behaviour. On top of this we have the global features of the brain such as the number of neurons, the number of glial cells (support cells), and the relationship between neurons. Every brain has a unique "network" or "web" of neuronal connections. Your memories, your skills, your behaviours, your processing patterns, are the gross product of information stored in the DNA of each microscopic neurone, and in the macroscopic network of the brain.

 

Pathology

• Brain diseases