What function do capillaries serve in the cardiovascular system?
Capillaries are thread-like, microscopic blood vessels that connect arteries and veins, delivering nutrients and oxygen to cells in the body and also helping to remove waste. Although invisible, these are the tiny vessels where the real exchanges for life occur.
In the human body, arteries and veins are like highways that carry blood. But it is the narrow side lanes that reach every home. In our human body, it is these capillaries that are those busy streets.
Read more about the function of capillaries, how they work, their types, and more.
How do capillaries work?
Based on the difference in pressure, gases, water, nutrients, and waste move in and out of these vessels.
They function in networks called capillary beds, which supply oxygen to cells according to their activity needs. It is within these capillary beds that exchange occurs.
The capillaries lack smooth muscles; therefore, the nearby vessel arterioles and metarterioles regulate blood flow by constricting and relaxing.
Local circulation within the capillaries is influenced by molecules that signal, such as nitric oxide, which promotes dilation, and endothelin, which promotes constriction.
How do capillaries help in transport?
A capillary consists of a network of vessels, each having an average length of 0.5 to 1mm.
The walls of the capillaries are thin and act like a membrane that allows small molecules, such as oxygen, carbon dioxide, water, glucose, fatty acids, and ketones, to pass through them.
Oxygen and food pass through the arteriolar end of the capillary unit; carbon dioxide and waste products move through the membrane into the vessel at the venous end of the capillary bed.
New capillaries are formed through vasculogenesis (creation of vessels from scratch) and later through angiogenesis (growth from existing vessels).
Types of capillaries
Based on different shapes, they carry out specific functions. Types of capillaries are
- Continuous fenestrated capillaries
They have small openings (called fenestrae) that allow quick exchange of substances. They are usually found in
- Kidneys, where waste products are removed
- Small intestine, where nutrients are absorbed
- Endocrine glands, where hormones are released
Continuous non-fenestrated capillaries
- They have a lining that allows small molecules to pass through and are usually found in the nervous system, fat, and muscle tissue.
- These capillaries protect our brain and allow only the most essential nutrients to cross.
Sinusoidal capillaries
- They have larger fenestrae, which allow substances to pass through them, and are usually found in the liver, spleen, and bone marrow.
Functions of capillaries
Capillaries serve a variety of organs and systems, such as.
- Transport new blood cells to enter the bloodstream from the bone marrow.
- Form a blood-brain barrier, they prevent toxins from crossing into the brain through the blood-brain barrier.
- Deliver hormones from the endocrine system to specific organs.
- Absorb excess water, salts, and sodium to form urine in the kidneys.
- Remove damaged red blood cells from the liver.
- Remove carbon dioxide and take in oxygen in the lungs.
- Transport nutrients to nourish the cells in the small intestine.
What happens when capillaries don’t work properly
- Port wine stains
- These birthmarks occur because of widened capillaries in the skin. The widening causes skin to appear pink or dark red in color and gradually darkens.
- The stains do not go away on their own, but they also do not spread to other areas.
- Petechiae
- Small, pinhead-like spots on the skin occur because of blood leaking into the skin. Petechiae may represent an underlying disease.
- Infectious diseases such as scarlet fever and meningococcal disease
- Trauma from straining while vomiting or coughing
- Leukemia
- Scurvy
- Low platelets
- Small, pinhead-like spots on the skin occur because of blood leaking into the skin. Petechiae may represent an underlying disease.
Rare diseases that occur when capillaries do not function properly are
- Systemic capillary leak syndrome (SCLS)
- There is no clear cause for this condition. It is considered that it may be related to a substance in the blood that damages capillary walls.
- In SCLS, the blood pressure drops quickly and requires emergency medical attention. Usually, it is accompanied by warning signs such as
- Nasal congestion
- Cough
- Nausea
- Lightheadedness
- Headache
- Fainting
- Arteriovenous malformation syndrome (AVM)
- It is a rare condition that is present at birth. It consists of a tangle of arteries and veins connected without capillaries. Although they can occur in any part of the body, they are usually found in the brain and spinal cord.
- They interfere with blood flow and oxygen delivery, and can even cause bleeding into the surrounding tissue. It can cause
- Headache
- Pain
- Weakness
- Seizures
- Vision, speech, and movement problems
- Microcephaly capillary malformation syndrome
- It is a rare genetic disorder caused by a mutation in the STAMBP gene, characterized by a small head and brain, as well as wide capillaries that appear as pink or red spots. Other features associated with the disease
- Seizures
- Developmental delays
- Distinct facial features
- Finger or toe abnormalities
- Growth delays
- It is a rare genetic disorder caused by a mutation in the STAMBP gene, characterized by a small head and brain, as well as wide capillaries that appear as pink or red spots. Other features associated with the disease
Clinical significance of capillary function
How do capillaries help to maintain homeostasis or the internal environment?
By continuously supplying nutrients and oxygen, they maintain the balance of fluids, gases, and electrolytes in tissues. The constant exchange ensures that every cell functions stably within its environment, which is essential for maintaining homeostasis.
Relevance to cardiovascular and systemic health
Healthy capillaries maintain the proper functioning of all organs in the heart and brain. They support high energy demands; any disruption in the capillary flow hampers organ functions, leading to systemic problems such as hypertension, diabetes complications, or ischemia.
Disease management
Capillary function helps preserve microcirculation and improve patient outcomes through early diagnosis.
Conclusion
Our heart and capillaries work continuously. Capillaries are like tiny threads, helping to exchange gases and nutrients, and transporting and clearing waste. They play a crucial role in our survival by providing us with oxygen, nutrition, and other essential substances, while also removing waste.
Here to answer all your questions
Capabilities get damaged when thin walls are weakened or stressed. Some important causes are
- The ultraviolet rays break down the collagen in the vessel walls, making them fragile.
- Aging causes a natural loss of elasticity in the capillaries, making them prone to breaking.
- Increased blood pressure causes stress and rupture of the vessels.
- Injury, trauma, or skin irritation breaks capillaries.
- Medical conditions like scurvy and diabetes damage capillaries.
- Smoking, alcohol, and a poor diet cause damage to capillary health.
Yes, capillaries can regenerate from pre-existing blood vessels by a process called angiogenesis, which restores blood flow to the tissues after injury or trauma.
Capillaries are thin and can be seen only under a microscope.
Capillaries are thin to facilitate the exchange of gases, nutrients, and waste products between the blood vessels and the surrounding tissue. Thin walls shorten diffusion distances, making exchange faster.
Yes, capillaries can regenerate from pre-existing blood vessels by a process called angiogenesis, which restores blood flow to the tissues after injury or trauma.
Capillaries differ from arteries and veins in several ways.
- Size and structure: Capillaries are one cell thick. At the same time, arteries and veins are thicker and have multiple layers of muscle and connective tissue.
- Functions: Arteries carry blood from the heart under pressure. Veins carry blood back to the heart under low pressure. Capillaries are exchange points between arteries and veins.
- Pressure and flow: In arteries, the blood flows under high pressure. In veins, the blood flows under low pressure with valves. Capillaries slow blood flow to allow the exchange of substances.
Special features: Arteries have muscular walls, while veins have valves that prevent backflow. Capillaries are thin and form networks to maximize exchange.
