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Equine Hormones and Respiratory System

Paper Type: Free Essay Subject: Biology
Wordcount: 2860 words Published: 18th May 2020

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Describe the structures of the equine respiratory system and give brief information about the functions of each structure. (250 words)

The respiratory system is responsible for, acid regulation, warming and clearing of inspired air, thermoregulation, defence against contaminations, and drawing air into the lungs therefore supplying oxygen to breath and transferring oxygen into from the air into the bloodstream. Functions of the respiratory system include; gaseous exchange, communication, thermoregulation, olfaction, humidify inspired air, defence against environmental contaminations, regularity of blood and excretion of waste. It also works to eliminate water when breathing out and is responsible for transferring carbon dioxide to the lungs and to provide sensory output. (Davis, 2019) states that “The upper respiratory tract includes the nostrils, nasal passages, pharynx, larynx and trachea. The lower respiratory tract includes the structures, which lie within the chest, the bronchi, bronchioles and alveoli in the lungs”.

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The airways (nostrils) allow the horse to breath. The nasal cavities is where the turbinate bones are housed. These are covered in mucous membranes to warm and filter incoming air into the horse. The pharynx is located at the back of the throat. This is where the epiglottis overlaps the soft palate, therefore allowing the horse to breath and when food is swallowed, the epiglottis covers the larynx and then the horse’s soft palate moves, therefore allowing food to pass to into the oesophagus instead of disturbing the breathing passage. The pharynx is a muscular tube which is shared by the respiratory system and the digestive system. It is formed by the nasopharynx and the oropharynx. The larynx is housed at the top of the trachea and “consists of interconnected cartilages, muscles and fibrous tissues covered by mucous membrane” (Brega, 1995, p.122).  The larynx is for producing a voice and ensuring only gas passes into the deep regions of the respiratory tract. “The trachea begins at the larynx and travels down the neck and into the thorax (chest). Within the thorax, the trachea divides into two tubes, the chief bronchi, each bronchus leading to one of the two lungs” (Oke, 2017). “The trachea’s soft tissue are kept open by almost complete rings of cartilage” (Hastie, 2001, p.55).

Bronchi’s, are tubes that are open by cartilage rings which each enter the lungs and then continue to branch out therefore becoming bronchioles. Bronchioles are narrow tubes lined with ciliated mucous membrane, they contain alveolar ducts which are air sacs which make up the lung tissue (Brega, 1995, p123).Alveoli have a structure specialised for efficient gaseous exchange, their walls are extremely thin and have a large surface area in relation to volume. They are fluid lined enabling gases to dissolve and they are surrounded by numerous capillaries.

Question Seven

(P3, M3) – Complete the table by filling in the name of the gland which produces each hormone and the main function of each.




Anterior Pituitary Gland

Thyroid stimulating hormone (TSH)

It is produced by the anterior pituitary gland, it stimulates the thyroid gland to release the hormones. It exerts its effects upon the thyroid gland and stimulates the production of the thyroid hormones, thyroxine, tri-iodothyronine and calcitonin. Tri-iodothyronine and Thyroxine control metabolic rate and are essential for normal growth. Thyrocalcitonin lowers blood calcium levels by increasing the activity of the osteoblasts, decreasing the activity of osteoclasts and reducing calcium update from the gastrointestinal tract.


Encourages lactation and “stimulates milk production from the udder after birth” (Davies, 2004). It stimulates the development of the mammary glands. (Thompson and Oberhaus 2015 p.343-353) states that “The secretion of prolactin in horses is affected by season, thyrotropin-releasing hormone, dopaminergic and antidopaminergic agents, exercise and stressful stimuli, meal feeding, oestrogen treatment, and antiopioidergic agents”.

Luteinising hormone (LH) 

Stimulates secretions of gonads, stimulates the ovaries. “The duration of secretion of LH in the mare and its associated ovulatory surge is considered to be longer than in most other animals” (Mottershead, 2001). LH rises at the beginning of estrus and unlike in other species, peaks 2 days post ovulation. In the mare, LH has a long half-life due to the sialic acid residues present. The final follicular rescue is LH dependent and the secretion of LH is modulated by endogenous oxytocin in estrus. It’s the female hormone that brings about ovulation and the development of the corpus luteum.

Follicle stimulating hormone

Stimulates secretions of gonads. The organ that it targets is the ovaries. The function is follicle development. It stimulates the ovaries and testes. FSH acts on the follicles in the ovaries to stimulate development and maturation. In the female it stimulates the development of the ovarian follicles. In the stallion, it stimulates sperm production.

Adrenocorticotrophic hormone (ACTH)

Controls the adrenal gland in the body and it effects the cortisol secretion. It controls the adrenal cortex. ACTH regulates the production of glucocorticoids from the adrenal gland. The ACTH controls the release of hormones from the adrenal cortex, makes steroid hormone. The cortisol prepares the body for stressful events and is a normal part of metabolism, however it can go wrong e.g. causing Cushing’s.

Somatotrophin (GH) 

Stimulates growth in the body by controlling the metabolism of sugars and fats digested and monitors the growth of the body’s tissues. Somatotropin is made by the anterior pituitary gland, known as the growth hormone, it controls epiphyseal bone growth and repair.

Posterior Pituitary Gland

Vasopressin (ADH) 

The ADH hormone acts on the kidneys and regulates the horse’s body hydration status. It effects the output of urine in the body.  Vasopressin affects the collecting ducts of the kidney nephron to help conserve water.


Oxytocin targets the smooth muscle in the uterus and has an effect on the uterine muscle contraction during the birth of a foal. The oxytocin encourages the let-down of milk during labour and also active for uterine contractions in the horse e.g. when foaling.

Thyroid Gland


The thyroid gland produces calcitonin and this helps the body’s blood regulate calcium, and helps lower it. Thyroid tissue is composed of two types of cells; follicular and parafollicular cells. Parafollicular cells, arranged in small groups in spaces between the hollow areas, these cells secrete the hormone in the horse called calcitonin (Davies, 2004, p.132).


Thyroxine promotes energy production and growth in the body. The thyroxine hormone also encourages sugar absorption in the intestines of the horse. “Thyroxin is secreted from the thyroid gland, which was known of for many years as an anatomical part-shaped like a shield- before its function as the source of this vital iodine compound hormone was discovered” (Hastie ,2001).


Parathyroid hormone (PTH)

The PTH hormone acts on the kidneys to reduce calcium excretion which then increasing phosphate excretion in the body. This then works to improve (raises) the levels of calcium in the blood. The PTH hormone encourages that calcium in absorbed from the horse’s intestine for the body. The PTH hormones promotes calcium absorption from the Intestine which involves vitamin d. “The main cells produce parathyroid hormone (PTH) whose main function is to regulate calcium levels in the body”(Norton,2013).It improves calcium levels by getting it from the diet from the intestinal wall or from the bones from the skeletal system. It also stimulates vitamin d activation and decreases the excretion of calcium absorption by the kidneys.


Adrenal Glands


They prepare the body for shock and helps reduced inflammations and effects of shock. “Cortisol controls the metabolism of fats, carbohydrates and proteins within the horse’s body” (Davies, 2004, p.134). “Cortisol together with another hormone, corticosterone, may reduce inflammatory reactions occurring within the body and may inhibit the immune system to a small extent” (Davies, 2004). The Glucocorticoids are released in times of stress to raise blood glucose levels.




Works to regulate the water balance in the horse. Aldosterone works to reduce the amount of sodium being excreted in the urine. Aldosterone affects the body’s ability to monitor and regulate the blood pressure in the horse. It sends signals and messages to organs like the kidneys, this can increase the levels of sodium the horse’s body sends to the bloodstream or the volume of potassium released in the urine.


Prepares the body for the flight and fight response and improves the blood flow to the muscles. They both assist with fright, fight and flight response connected to the sympathetic nervous system. “Adrenaline is the stimulator of the sympathetic nervous system and noradrenalin is the produces a similar action, but slightly more slowly” (Hastie, 2001).





The breakdown of glycogen which in term raises the blood glucose level in the body. “Glucagon raises blood sugar levels by pulling reserves out of storage when circulating energy supplies begin to dwindle “(Kilby, 2007).


Encourages the muscles to use glucose correctly, therefore using the glucose and which causes the glucose level to lower in the blood. “Insulin, the primary modulator of blood-sugar (glucose) concentration, acts swiftly after food intake to limit the liver’s production of glucose and increase stored energy (glycogen) in that organ, to facilitate increased protein synthesis, to convert un-needed energy to fat for storage in body tissues and possibly to control appetite”(Kilby, 2007).


Oestrogen and progesterone 

They both play a major role in the oestrus cycle in the horse It works in the uterus and genital tract. The oestrus cycle will last days or weeks.                                                                                                                                                                                                    The oestrogen works to effects the dioestrus and pregnancy. The oestrogen hormone is produced by the follicle. The progesterone hormone is produced by the corpus luteum and effects the oestrous behaviour and lubrication of the genital tract. Progesterone is from the transformed granulosa cells (or thecal cells in the mare) and rises shortly after ovulation. It is the dominant hormone of diestrus. There are two cycle phases; oestrous (in heat) and dioestrus (out of heat).



Testosterone is what makes the horse develop correctly and is also responsible for the horse’s characteristics. “Testosterone is the primary androgen, or male hormone which maintains sperm production, contributes to secondary sex characteristics and fires libido” (Kilby, 2007). Testosterone is responsible for the increased musculature of stallions because it has an anabolic effect” (Davies,  2004)




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