Circulatory System (part 3). A&P 1 Tutor: Eleshia Howell. Portal circulation. Instead of the venous blood returning directly, through one capillary bed, the portal system offers a second filtering system for the blood from digestive organs.
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Tutor: Eleshia Howell
The high concentration of nutrients absorbed from the stomach and intestines is first received by liver, which then regulates blood nutrient level and performs numerous chemical modifications.
Placenta is attached to the baby via umbilical cord which contains two arteries and one vein. The cord enters the foetus at the abdomen (umbilicus).
Placenta also has essential endocrine function in that it secretes the hormones that maintain pregnancy ~ hCG, Progesterone and Oestrogen.
Foramen ovale – a valve-like opening that allows blood to flow between the right and left atria, again so that most blood bypasses foetal lungs.
CHANGES AT BIRTH:
Once the placental circulation ceases soon after birth, the umbilical vein & arteries, plus ductusvenosus automatically collapse.
SHOCK (circulatory failure) – occurs when the metabolic needs of cells are not being met because of inadequate blood flow. Essentially, a reduction in circulating blood volume, in blood pressure and in cardiac output.
This causes tissue hypoxia, and inadequate supply of nutrients and the accumulation of waste products.
There are various kinds of shock:
Hypovolaemic shock – occurs when blood volume is reduced by 15-25%. This may be caused by severe haemorrhage, extensive burns, severe vomiting or diarrhoea.
In the short term, there are physiological attempts to restore an adequate blood supply, eg sympathetic activation, release of ADH and renin-angiotensin-aldosterone reflex. Medical interventions may also help to restore perfusion to the brain and heart and therefore restore physiological balance.
In severe cases, the cycle of hypoxia, progressive acidosis and tissue death results in organ failure, circulatory collapse, brain stem damage and ultimately death.
Embolus – a mass of any material carried in the blood, eg blood clot, tumour fragments, arterial plaque, air, pus, fat (from bone fractures), nitrogen bubbles (the ‘bends’). An embolus may interrupt blood supply or completely obstruct a vessel.
Atherosclerosis – accumulation of fatty plaques in the arteries; may cause partial or complete obstruction of an artery.
Varicose veins – when a vein is so dilated that the valves can not close to prevent backflow, causing a loss of elasticity and giving the appearance of elongated, tortuous and fibrous veins. This condition may be hereditary or caused by age, pregnancy, pressure, obesity, poor venous return. Most commonly occurs in the legs, but can also happen around rectum/anus (haemorrhoids), vagina / scrotum, oesophagus.
Heart failure – when the cardiac output is unable to maintain the circulation of sufficient blood to meet the needs of the body. May occur on either side of the heart (more common in left ventricle due to workload) but will eventually effect the whole organ. Over time, the heart chambers will become thicker and enlarge and the R-A-A system becomes activated leading to salt and water retention, which in turn increases blood volume and cardiac workload!
Arrhythmias – alterations to the normal heart rate generated by the conducting system of the heart.
Hypertension – high blood pressure. May be of gradual onset, due to aging, linked to hereditary, lifestyle, diet, disease factors. Commonly effects the kidneys, brain, heart, blood vessels and eyes. 140/90 and beyond is considered hypertensive.