Active transport is reliant on carrier proteins and thus follows the same rules as facilitated diffusion in that they are specific have a maximum rate and are subject to competition. Crucially they transport substances against their concentration gradient and so require energy to work.
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The adrenal glands are paired bodies lying cranial to the kidneys within the retroperitoneal space. The glands consist of two layers; the cortex and medulla.
The anus is the terminal portion of the alimentary tract which communicates with the external environment. Two sphincters control it's aperture. It allows faeces and gas to leave the body. Defeacation is the process where faeces are expelled from the rectum through the anus.
The Blood Brain Barrier refers to the mechanisms in place around the microvasculature of the brain to ensure optimal neural functioning. Endothelial cells are the structural basis of the blood brain barrier and are joined by tight cellular junctions formed by the transmembrane proteins the occludins and the claudins.
Osteogenesis is the formation of bone. Bone forms from one of three lineages; the skull forms from the neural crest; the limb skeleton forms from the lateral plate mesoderm; and the axial skeleton forms from the paraxial mesoderm (sclerotome).
The Bursa of Fabricus is a primary lymphoid organ found in birds. The bursa was the first place that a certain subset of lymphocytes was observed and consequently they were named B lymphocytes (bursa of Fabricius or bursa equivalent organs). The bursa is involved in the differentiation of B lymphocytes.
Blood is supplied to the brain from a ventral arterial supply in all species; from a circle of arteries called the Circle of Willis (also called the cerebral arterial circle or arterial circle of Willis) which lies ventrally to the hypothalamus where it forms a loose ring around the infundibular stalk. Although the appearance of the circle of Willis is fairly constant amongst mammals, the sources of blood supply to the circle and the direction of flow around the circle are very species specific. Blood is supplied to the brain by the internal carotid artery in dogs and horses whilst in other domestic species the main blood supply is from branches of the maxillary artery.
The cecum is a blind ending diverticulum of the large intestine and it exists at the junction of the ileum and the ascending colon. Its size and physiological importance varies between species. It is a site of microbial fermentation, absorption and transportation.
Each mammary complex consists of 5-20 mammary units and their corresponding ducts. The ducts open separately on the tip of the teat. Shallow grooves indicate the border between complexes. An intermammary sulcus divides the right from the left row.
The lower urinary tract is the collection of organs which convey the formed urine from the kidneys to the exterior of the body. The urine is not altered in this part of the system in species other than the horse (where mucous is added) but instead its function is to collect and store the urine until enough of it is collected for release to become necessary. This gives the animal urinary continence. Three major structures make up this tract. The ureters, the bladder and the urethra.
Also referred to as the reticuloendothelial system or mononuclear phagocytic system. It is comprised of primary lymphoid organs (bone marrow, Bursa of Fabricius, the foetal liver and the thymus) which are responsible for the production of lymphocytes, and the secondary lymphoid organs (lymph nodes, spleen and mucosal associated lymphoid tissue) which function to provide an environment where lymphocytes can react to antigen from the tissue fluid, blood and mucosal surfaces.
Embryo, when applied to mammals, is the term given to the developing organism from fertilisation to birth. Developmental biology, or embryology, is the study of the embryo as it transforms from a unicellular zygote to a multicellular, mulitsystemed organism which in some cases is ready to function autonomously at birth. Developmental biology is of interest to vets in understanding why organs and systems are the way they are, but also in understanding genetic diseases and applying cell based therapies to treat loss or damage to tissues.
Comprised of a group of duct-less glands with limited or no anatomical contact with each other, the endocrine system integrates and controls metabolic activity through the secretion of hormones into the vascular system. These hormones may have their effects on tissues and organs far from where they were produced.
The mammary gland is a modified sweat gland that nourishes the young. It consists of the mamma and the teat. Undeveloped in both the male and female at birth, the female mammary gland begins to develop as a secondary sex characteristic at puberty.
The mediastinum divides the thoracic cage into two halves. It extends from the Spine to the Sternum and contains many structures including blood vessels, nerves, oesophagus, trachea and heart.
The enlarged swelling of the gastrointestinal tract between the oesophagus and the duodenum is called the stomach. It is a simple structure in carnivores and a compound structure in ruminants. The stomach functions as a reservoir of food where digestion occurs through chemical and mechanical processes. This allows food to be broken down further and absorbed.
Olfaction is the sense of smell, which is the ability to perceive and distinguish odours. Most mammals have a good sense of smell, but most birds generally do not. The sense of smell is well-developed in carnivores (predators) and ungulates (prey). Fish also have a fairly well-developed sense of smell. Olfactory and gustatory receptors can combine to contribute to flavour.
The oesophageal groove is present in newborn ruminants. It is a channel taking milk from the oesophagus into the abomasum, bypassing the rumen, reticulum and omasum.
The oesophagus (or gullet) is a muscular tube which transports food from the pharynx to the stomach. A bolus of food is passed down the oesophagus by peristalsis. The oesophagus is divided into cervical, thoracic and abdominal sections.